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Acquired methemoglobinemia is a treatable condition that is often clinically subtle and can be missed on routine clinical assessment. We present a 73-year-old male who was evaluated in the emergency department with worsening respiratory symptoms requiring oxygen. He tested COVID-19 positive and had new pulmonary emboli evident on his CT chest. The patient was on dapsone therapy as a treatment for bullous pemphigoid. The discrepancy between his oxygen levels on the pulse oximeter and blood gas was noted and was treated with 3% methylene blue for dapsone-induced methemoglobinemia. The patient received treatment for COVID-19 pneumonia and pulmonary emboli. Our case demonstrates that dapsone-induced methemoglobinemia can present concomitantly with other more common causes of acute hypoxic respiratory failure. It is noteworthy for physicians to maintain a high index of suspicion for oxygen level discrepancy in hypoxic patients and consider the possibility of acquired methemoglobinemia. Hence, earlier detection and treatment of the etiology of tissue hypoxia., Competing Interests: The authors have declared that no competing interests exist., (Copyright © 2024, Alhusari et al.)

Drug-induced liver injury is a common cause of acute liver failure. Dapsone is increasingly used in combination with rifampicin for the treatment of leprosy and also for several dermatological disorders. Clinically, abnormal liver function and focal bile duct destruction were reported after dapsone therapy. Lagerstroemia speciosa Pers., commonly known as Banaba has been traditionally used to treat various ailments including diabetes and obesity due to its antioxidant and anti-inflammatory efficacies. This study investigated the hepatoprotective effect of ethanolic banaba leaves extract (EBLE) against dapsone-induced hepatotoxicity in rats. Dapsone (30 mg/kg, i.p.) was administered twice daily for 30 days. In separate groups, rats were post-treated orally with EBLE (250 and 500 mg/kg) and silymarin (100 mg/kg) once daily for 30 days after dapsone administration. The marker enzymes of hepatotoxicity, oxidative stress markers, inflammatory markers and histopathology of liver were done. HPTLC analysis confirmed the presence of 12.87 µg of corosolic acid per mg of EBLE. Dapsone administration-induced significant ( p  < 0.001) elevation of marker enzymes of hepatotoxicity in serum. This treatment also increased lipid peroxidation ( p  < 0.001) and pro-inflammatory markers (tumor necrosis factor-alpha, transforming growth factor-beta, and nuclear factor kappa-B) expressions ( p  < 0.001) and decreased antioxidants ( p  < 0.001) such superoxide dismutase, catalase and glutathione in the liver tissue. All these abnormalities were significantly ( p  < 0.001) mitigated after EBLE (500 mg/kg) and silymarin post-treatments. The results of this study suggest that silymarin and EBLE can be used for dapsone-induced hepatotoxicity.

Dapsone hydroxylamine (DDS-NHOH), N-hydroxylated metabolite of a sulfonamide antibiotic, dapsone, is responsible for various adverse effects of dapsone that include methemoglobinemia, hemolytic anemia, and thrombosis. However, the mechanism underlying DDS-NHOH-induced thrombosis remains unclear. Here, we demonstrated that DDS-NHOH, but not dapsone, could increase prothrombotic risks through inducing the procoagulant activity of red blood cells (RBCs). In freshly isolated human RBCs in vitro, sub-hemolytic concentrations of DDS-NHOH (10-50 μM) increased phosphatidylserine (PS) exposure and augmented the formation of PS-bearing microvesicles (MV). Reactive oxygen species (ROS) generation and the subsequent dysregulation of enzymes maintaining membrane phospholipid asymmetry were found to induce the procoagulant activity of DDS-NHOH. Dapsone hydroxylamine also accelerated thrombin generation and enhanced RBC self-aggregation and adherence of RBCs to endothelial cells in vitro. Most importantly, both the single dose of 50 or 100 mg/kg (i.p.) DDS-NHOH and repeated doses of 10 mg/kg per day (i.p.) for 4 days increased thrombus formation in rats (six rats per dose) in vivo, substantiating a potential prothrombotic risk of DDS-NHOH. Collectively, these results demonstrated the central role of RBC procoagulant activity induced by DDS-NHOH in the thrombotic risk of dapsone., (© The Author(s) 2019. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Aim: To optimize the production of pH-sensitive dapsone (DAP) nanoparticles based on Eugradit L100 (NPs-EL100-DAP) for oral delivery., Materials & Methods: NPs-EL100-DAP were optimized using a Plackett-Burman design and a Box-Behnken design. The physicochemical properties of the obtained nanoparticles were monitored by microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, differential scanning calorimetry, in vitro release assays, and examined for cytotoxicity and permeation across intestinal barrier., Results: The in vitro release assay of NPs-EL100-DAP confirmed the nanoparticles' pH sensitivity and the ability to deliver DAP at intestinal environment. NPs-EL100-DAP demonstrated enhanced intestinal interactions in comparison to free DAP, across Caco-2 monolayers., Conclusion: These studies demonstrate the potential of NPs-EL100-DAP as a therapeutic platform for oral treatment of leprosy.

Aczone gel 5% contains dapsone and is a commonly used topical dermatologic therapy for acne in adolescents and adults. We describe the first reported pediatric case of a previously healthy girl presenting with acute onset of methemoglobinemia after exposure to her sibling's Aczone gel. The patient was successfully treated with methylene blue initially and subsequently needed an additional dose for rebound methemoglobinemia. This case demonstrates the complications of systemic absorption of dapsone in the pediatric population resulting in clinically significant methemoglobinemia from a single topical application., (Copyright © 2016 by the American Academy of Pediatrics.)

Pneumocystis carinii pneumonia (PCP) is a major opportunistic infection that affects patients with human immunodeficiency virus. Although orally administered dapsone leads to high hepatic metabolism, decreasing the therapeutic index and causing severe side effects, this drug is an effective alternative for the treatment of PCP. In this context, microencapsulation for pulmonary administration can offer an alternative to increase the bioavailability of dapsone, reducing its adverse effects. The aim of this work was to develop novel dapsone-loaded chitosan microcapsules intended for deep-lung aerosolized drug delivery. The geometric particle size (D 4,3) was approximately 7 μm, the calculated aerodynamic diameter (d aero) was approximately 4.5 μm, and the mass median aerodynamic diameter from an Andersen cascade impactor was 4.7 μm. The in vitro dissolution profile showed an efficient dapsone encapsulation, demonstrating the sustained release of the drug. The in vitro deposition (measured by the Andersen cascade impactor) showed an adequate distribution and a high fine particles fraction (FPF = 50%). Scanning electron microscopy of the pulmonary tissues demonstrated an adequate deposition of these particles in the deepest part of the lung. An in vivo toxicity experiment showed the low toxicity of the drug-loaded microcapsules, indicating a protective effect of the microencapsulation process when the particles are microencapsulated. In conclusion, the pulmonary administration of the novel dapsone-loaded microcapsules could be a promising alternative for PCP treatment.

Dapsone is a sulfone-type drug used widely for different infectious, immune, and hypersensitivity disorders as an antibacterial treatment alone or in combination for leprosy and sometimes for infected skin lesions. DHS is a severe idiosyncratic adverse reaction with multi-organ involvement. However, acute necrotic hepatitis requiring an emergent LT is rare. Herein, we report a case of 12-yr-old girl who suffered from fulminant hepatitis and multi-organ failure due to DHS for PPD. She was saved by emergent LDLT. A high index of suspicion and rapid diagnosis are necessary not to miss this potentially lethal but rare disease., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

There was performed a study of carcinogenicity of benzidinsulfon (4.4'-diaminodiphenil sulfone) in rats and mice. Experimental animals (99 mice and 99 rats, approximately equally divided by sex) received the drug throughout the life by subcutaneous injections (once a week) or addition to food (5 times a week). A single dose per animal in rats was: subcutaneous administration--50 mg (in females it was reduced due to the toxicity after beginning of the experiment to 25 mg) in 0.5 ml of oil, while feeding--20 mg in 0 5 ml of oil; in mice--respectively 5 mg in 0.2 ml of oil, and 2 mg in 0, 2 ml of oil. The maximum amount of a substance when administered subcutaneously to male rats was 5.65 g, to female rats--2, 68 g, when fed to rats 12.44 g, when injected subcutaneously in mice--380 mg, when fed--737 mg. The survival of experimental animals was significantly reduced as compared to the intact control because of the toxic effect of the drug, preferably chronic nephrosis with nephritic component and secondary nephrosclerosis and as well as miocardiosclerosis and aortic sclerosis. Frequency and timing of detection of tumors in experimental animals was not significantly different from that observed in the control that indicated the absence of carcinogenic features of benzidinsulfon.

Background and Purpose: N-hydroxylation of dapsone leads to the formation of the toxic hydroxylamines responsible for the clinical methaemoglobinaemia associated with dapsone therapy. Dapsone has been associated with decreased lifespan of erythrocytes, with consequences such as anaemia and morbidity in patients treated with dapsone for malaria. Here, we investigated how dapsone and/or its hydroxylamine derivative (DDS-NHOH) induced erythrocyte membrane alterations that could lead to premature cell removal., Experimental Approach: Erythrocytes from healthy donors were subjected to incubation with dapsone and DDS-NHOH for varying times and the band 3 protein tyrosine-phosphorylation process, band 3 aggregation, membrane alteration and IgG binding were all examined and compared with erythrocytes from two patients receiving dapsone therapy., Key Results: The hydroxylamine derivative, but not dapsone (the parent sulphone) altered membrane protein interactions, leading both to aggregation of band 3 protein and to circulating autologous antibody binding, shown in erythrocytes from patients receiving dapsone therapy. The band 3 tyrosine-phosphorylation process can be used as a diagnostic system to monitor membrane alterations both in vitro, assessing concentration and time-dependent effects of DDS-NHOH treatment, and in vivo, evaluating erythrocytes from dapsone-treated patients, in resting or oxidatively stimulated conditions., Conclusions and Implications: DDS-NHOH-induced alterations of human erythrocytes can be directly monitored in vitro by tyrosine-phosphorylation level and formation of band 3 protein aggregates. The latter, together with antibody-mediated labelling of erythrocytes, also observed after clinical use of dapsone, may lead to shortening of erythrocyte lifespan., (© 2010 The Authors. British Journal of Pharmacology © 2010 The British Pharmacological Society.)

The most prominent adverse effects seen during treatment with dapsone, an antibacterial and antiprotozoal agent, are hemolysis and methemoglobinemia. An in vitro microsomal/cytochrome P(450) (CYP)-linked assay, which allows reactive metabolites generated in situ to react with the co-incubated human erythrocytes, was employed to profile CYP isoforms responsible for hemotoxicity of dapsone. Dapsone caused a robust generation of methemoglobin in human erythrocytes in the presence of human/mouse liver microsomes, which indicates contribution of CYP-mediated metabolism for hemotoxicity. The highest methemoglobin formation with dapsone was observed with CYP2C19, with minor contributions from CYP2B6, CYP2D6 and CYP3A4. Cimetidine and chloramphenicol completely abrogated methemoglobin generation by dapsone, thus confirming a predominant contribution of CYP2C19. The results provide useful insights into CYP-dependent hemotoxicity of dapsone in human erythrocytes., ((c) 2009 John Wiley & Sons, Ltd.)

Allergen Inc has launched Aczone, a topical gel formulation of the antibacterial, anti-inflammatory agent dapsone, for the potential treatment of acne vulgaris. Oral dapsone has demonstrated efficacy in acne, but was associated with severe side effects such as anemia, which was particularly serious in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Aczone was developed to overcome this limitation, and is formulated using solvent-microparticle technology for improved absorption and action and for fewer side effects. In a phase I clinical trial, systemic exposure to dapsone was 126-fold lower following treatment with Aczone compared with oral dapsone. Aczone significantly reduced lesion counts in patients with acne in phase III trials, and was particularly effective in reducing inflammatory lesions. In a phase IV trial, Aczone was safely applied to patients with G6PD deficiency without inducing anemia. Phase IV trials in patients with acne were ongoing at the time of publication to assess safety and to compare Aczone monotherapy with combinations of Aczone and other anti-acne therapeutics. At the time of publication, Allergen was also developing Aczone for the treatment of rosacea; the drug was undergoing phase II trials for this indication. Aczone appears to be a novel promising anti-acne therapeutic option, particularly for patients with inflammatory acne.

In adults with immune thrombocytopenic purpura (ITP), steroids are usually proposed as first-line therapy, but long-term complete responses are obtained in no more than 20% of patients. For the remaining patients, splenectomy is considered the treatment of choice, with reported "cure" rates from 60-70%. However, the inherent risks of surgery and sepsis after splenectomy without a guarantee of success justify the search for strategies aimed to avoid splenectomy. Here we retrospectively evaluated the results of dapsone treatment in ITP patients that failed first-line therapy with steroids. These patients received dapsone 100 mg/day for a minimum of 30 days before splenectomy was considered. Efficacy was defined as a sustained rise in platelet counts (>50 x 10(9)/l) clearly attributed to dapsone treatment. Among 52 steroid-dependent or refractory patients, dapsone resulted in sustained increases in platelet counts in 44.2% of patients, after a median follow-up of 21.10 months after treatment initiation. The long-term efficacy of dapsone in this setting is further corroborated by the observation that none of the "responding" patients required splenectomy in the follow-up, compared to 69.0% of the "non-responding" patients. Dapsone-related adverse events were mild and promptly reversed by treatment withdrawal. The results of our retrospective analysis suggest that dapsone is a safe and effective second-line agent for steroid-dependent or refractory ITP patients. Because of its well-known safety profile and low cost compared to other potential second-line treatments for ITP, a trial course of dapsone should be viewed as an attractive option before splenectomy in steroid-dependent of refractory adult ITP patients.

Aim of the Study: Chi-Zhi-Huang decoction (PGR) is one of the traditional Chinese medicine (TCM) preparations with unique effect on withdrawing jaundice and has been used to treat icteric patients in China for many years. In this research, we aim at to evaluate the potential activity of PGR in restoring hepatic drug metabolism in a damaged liver., Materials and Methods: A cocktail approach with caffeine (10mg/kg), dapsone (10mg/kg) and chlorzoxazone (20mg/kg) respectively as probe drug of cytochrome P450 (CYP) isoform of CYP 1A2, 3A4 and 2E1 was used to evaluate its possible effects on Phase I oxidative metabolism. Pretreated with three dosages of PGR water extract (0.75, 1.5 and 3g/kg, po) for 5 days, male Wistar rats (220-240 g) were intoxicated by phenylisothiocyanate (PITC, 100mg/kg, po) 24h before probes intravenous injection. The pharmacokinetics of the probes in the blood was determined simultaneously by HPLC, and their non-compartmental parameters were used to evaluate the metabolic difference among the groups. Moreover, the levels of liver enzymes (ALT, AST, ALP) and bilirubins were also measured for insight of liver function., Results: The findings in this study suggest that PGR induces CYP 3A4, does not have much effect on CYP 2E1, and inhibits CYP 1A2 at high dosage., Conclusion: The current pharmacokinetic approach allowed the protective effects of PGR on oxidative drug metabolism in damaged liver to be systemically examined and will certainly help in the explanation of synergistic effect of the composites formula.

The initiation of an immune response to small molecules is believed to require the release of stress/danger signals that activate resident dendritic cells, presumably secondary to the formation of reactive metabolites. We hypothesized that exposure to arylhydroxylamine metabolites of dapsone and sulfamethoxazole lead to the expression/release of numerous stress signals in the skin. To test this hypothesis, we examined the effect of these metabolites on the expression of selected heat shock proteins, uric acid, cytokines, adhesion molecules, and costimulatory molecules in normal human epidermal keratinocytes (NHEKs). NHEKs showed a time-dependent up-regulation of heat shock protein 70 and translocation of heat shock protein 27 when exposed to the arylhydroxylamine metabolites. In addition, the secretion of several proinflammatory cytokines was increased upon incubation of these cells with metabolite. In contrast, the uric acid concentration was not altered. Moreover, intercellular adhesion molecule-1, CD80, and CD86 expressions did not change when NHEKs were exposed to these reactive metabolites. Our data suggest that NHEKs selectively up-regulate certain danger signals when exposed to arylhydroxylamine metabolites. These signals may subsequently activate dendritic cells and initiate an immune response within skin.

Cutaneous drug reactions (CDRs) associated with sulfonamides are believed to be mediated through the formation of reactive metabolites that result in cellular toxicity and protein haptenation. We evaluated the bioactivation and toxicity of sulfamethoxazole (SMX) and dapsone (DDS) in normal human dermal fibroblasts (NHDF). Incubation of cells with DDS or its metabolite (D-NOH) resulted in protein haptenation readily detected by confocal microscopy and ELISA. While the metabolite of SMX (S-NOH) haptenated intracellular proteins, adducts were not evident in incubations with SMX. Cells expressed abundant N-acetyltransferase-1 (NAT1) mRNA and activity, but little NAT2 mRNA or activity. Neither NAT1 nor NAT2 protein was detected. Incubation of NHDF with S-NOH or D-NOH increased reactive oxygen species formation and reduced glutathione content. NHDF were less susceptible to the cytotoxic effect of S-NOH and D-NOH than are keratinocytes. Our studies provide the novel observation that NHDF are able to acetylate both arylamine compounds and bioactivate the sulfone DDS, giving rise to haptenated proteins. The reactive metabolites of SMX and DDS also provoke oxidative stress in these cells in a time- and concentration-dependent fashion. Further work is needed to determine the role of the observed toxicity in mediating CDRs observed with these agents.

Sulphonamides, such as sulphamethoxazole (SMX) and the related sulphone dapsone (DDS), show a higher incidence of cutaneous drug reactions (CDRs) in patients with the acquired immunodeficiency syndrome (AIDS) compared with human immunodeficiency virus (HIV) negative patients. During HIV infection, pro-inflammatory cytokines such as interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) are increased. We hypothesized that this increase in pro-inflammatory cytokines may increase the toxicity of the arylhydroxylamine metabolites of SMX (S-NOH) and DDS (D-NOH) in keratinocytes through a reduction in glutathione (GSH) content. We evaluated the effect of TNF-alpha on GSH levels in normal human epidermal keratinocytes (NHEK) and found a significant decrease in GSH after 24h. Pre-treatment with TNF-alpha also resulted in an increase in the recovery of D-NOH, but failed to alter drug-protein covalent adduct formation in NHEK. We also evaluated the effect of TNF-alpha, IL-1 beta, interferon-gamma (IFN-gamma), lipopolysaccharide (LPS) and conditioned media (obtained from monocytes stimulated with LPS) on the cytotoxicity of pre-formed arylhydroxylamine metabolites in NHEK. Priming cells with cytokines did not significantly alter the cytotoxicity of the metabolites. The effect of pre-treatment with TNF-alpha on reactive oxygen species (ROS) generation in NHEK was also determined. While ROS formation in NHEK was increased in the presence of D-NOH, TNF-alpha did not alter the level of ROS generation. Our data suggest that the level of GSH reduction induced by pro-inflammatory cytokines does not predispose NHEK to cellular toxicity from either S-NOH or D-NOH.

Many adverse drug reactions are caused by the cytochrome P450 (CYP) dependent activation of drugs into reactive metabolites. In order to reduce attrition due to metabolism-mediated toxicity and to improve safety of drug candidates, we developed two in vitro cell-based assays by combining an activating system (human CYP3A4) with target cells (HepG2 cells): in the first method we incubated microsomes containing cDNA-expressed CYP3A4 together with HepG2 cells; in the second approach HepG2 cells were transiently transfected with CYP3A4. In both assay systems, CYP3A4 catalyzed metabolism was found to be comparable to the high levels reported in hepatocytes. Both assay systems were used to study ten CYP3A4 substrates known for their potential to form metabolites that exhibit higher toxicity than the parent compounds. Several endpoints of toxicity were evaluated, and the measurement of MTT reduction and intracellular ATP levels were selected to assess cell viability. Results demonstrated that both assay systems are capable to metabolize the test compounds leading to increased toxicity, compared to their respective control systems. The co-incubation with the CYP3A4 inhibitor ketoconazole confirmed that the formation of reactive metabolites was CYP3A4 dependent. To further validate the functionality of the two assay systems, they were also used as a "detoxification system" using selected compounds that can be metabolized by CYP3A4 to metabolites less toxic than their parent compounds. These results show that both assay systems can be used to screen for metabolic activation, or de-activation, which may be useful as a rapid and relatively inexpensive in vitro assay for the prediction of CYP3A4 metabolism-mediated toxicity.

Lipid peroxidation and the accompanying translocation of phosphatidylserine (PS) from the inner to the outer leaflet of the lipid bilayer have recently been identified as key components of a signaling pathway for phagocytosis of apoptotic cells by macrophages. Drug-induced hemolytic anemia has long been known to be caused by an accelerated uptake of damaged (but intact) erythrocytes by macrophages in the spleen, and this process has been associated with enhanced formation of reactive oxygen species (ROS). However, the role of lipid peroxidation in hemolytic injury has remained unclear, and the effect of hemolytic agents on the distribution of PS in the erythrocyte membrane is unknown. The present studies were undertaken to determine whether lipid peroxidation and PS translocation could be detected in rat and human erythrocytes by three types of direct-acting hemolytic agents--dapsone hydroxylamine, divicine hydroquinone, and phenylhydrazine. 2',7'-Dichlorodihydrofluorescein diacetate was employed as a probe for intracellular ROS formation; lipid peroxidation was assessed by GC/MS analysis of F2-isoprostanes; and PS externalization was measured by annexin V labeling and the prothrombinase assay. The data confirmed that all three hemolytic agents generate ROS within erythrocytes under hemolytic conditions; however, no evidence for lipid peroxidation or PS translocation was detected. Instead, ROS production by these hemolytic agents was associated with extensive binding of oxidized and denatured hemoglobin to the membrane cytoskeleton. The data suggest that the transmembrane signal for macrophage recognition of hemolytic injury may be derived from oxidative alterations to erythrocyte proteins rather than to membrane lipids.

Data on 90 patients (55 adults and 35 children) with chronic idiopathic thrombocytopenic purpura (ITP) and a platelet count of <50 x 10(9)/L treated with dapsone at a dose of 1-2 mg/kg/d are presented. A response was observed in 57 (63.3%) patients. The average time for response was 3.5 months (range 1-9) and the average duration of treatment with dapsone was 10.4 months (range 4-14). Overall response rates of 65.7% and 61.8% were observed in children and adults respectively. Side effects requiring discontinuation of therapy were observed in three (2%) patients. These results demonstrate that dapsone is an effective, inexpensive and well-tolerated treatment for chronic ITP, in both children and adults and could be considered for patients who fail steroid therapy.

Cutaneous drug reactions (CDR) are responsible for numerous minor to life-threatening complications. Though the exact mechanism for CDR is not completely understood, evidence suggests that bioactivation of drugs to reactive oxygen or nitrogen species is an important factor in the initiation of these reactions. Several CDR-inducing drugs having an arylamine functional group, such as sulfamethoxazole (SMX) and dapsone (DDS), undergo bioactivation to reactive arylhydroxylamine metabolites. These metabolites can generate cellular oxidative stress by forming reactive oxygen species (ROS). Several studies have demonstrated a higher cytotoxicity with DDS hydroxylamine (DDS-NOH) compared to SMX hydroxylamine (SMX-NOH). To investigate the role of differential ROS generation in the higher cytotoxicity of DDS-NOH, hydroxylamine metabolites of SMX and DDS were synthesized and ROS formation by these metabolites determined. DDS-NOH and its analogues/metabolites consistently resulted in higher ROS formation as compared to SMX-NOH. However, comparison of the ROS generation and cytotoxicity of a series of arylhydroxylamine analogues of DDS did not support a simple correlation between ROS generation and cell death. Numerous ROS scavengers were found to reduce metabolite-induced ROS formation, with differences in the potency between the agents. The decrease in DDS-NOH-induced ROS generation in NHEK with ascorbic acid, N-acetylcysteine, Trolox, and melatonin was 87, 86, 44, and 16%, respectively. Similarly, the cytotoxicity and adduct formation of DDS-NOH in NHEK was reduced in the presence of ascorbic acid. In summary, these studies show that arylhydroxylamine metabolites of SMX/DDS induce ROS generation in NHEK, though such generation is not directly related to cytotoxicity.

The artemisinins are playing an increasingly important role in treating multidrug-resistant malaria. The artemisinin, artesunate, is currently in use in Southeast Asia and is advocated for use in Africa. In these areas, more than one million people die of malaria each year, with the highest mortality occurring in children and pregnant women. To test the developmental toxicity in ICH-compliant animal studies, embryofetal development studies were conducted in rats and rabbits treated with artesunate alone or a three-drug combination (CDA) consisting of chlorproguanil hydrochloride, Dapsone, and artesunate in the ratio 1.00:1.25:2.00. Developmental toxicity seen with CDA could be attributed to the administered dose of artesunate. The hallmark effect of artesunate exposure was a dramatic induction of embryo loss, apparent as abortions in rabbits and resorptions in both rats and rabbits. In addition, low incidences of cardiovascular malformations and a syndrome of skeletal defects were induced at or close to embryolethal doses of artesunate in both rats and rabbits. The cardiovascular malformations consisted of ventricular septal and vessel defects. The skeletal syndrome consisted of shortened and/or bent long bones and scapulae, misshapen ribs, cleft sternebrae, and incompletely ossified pelvic bones. These developmental effects were observed largely in the absence of any apparent maternal toxicity. The no or low adverse effect levels were in the range of 5 to 7 mg/kg/day artesunate. Encouragingly, no adverse drug-related developmental effects have been observed in a limited number of pregnant women (more than 100 first trimester and 600 second and third trimester) treated with artemisinins, primarily artesunate. Investigations of the mechanism of developmental toxicity are ongoing to attempt to determine whether rats and rabbits are more sensitive to artemisinins than humans., (Copyright 2004 Wiley-Liss, Inc.)

Dapsone (DDS) (4,4'diaminodiphenylsulfone), the drug of choice for the treatment of leprosy, frequently induces haemolytic anaemia and methaemoglobinaemia. N-hydroxylation, one of the major pathways of biotransformation, has been constantly related to the methaemoglobinaemia observed with the use of the drug. In order to determine the reversible inhibition of this toxicologic bioactivation pathway without changing the detoxification pathways of the drug or cytosolic acetylation, cimetidine (CIM), ranitidine and famotidine were administered in combination with DDS to male Wistar rats weighing 200-220 g. The animals were divided into nine groups of eight: group 1 received a single dose of 40 mg kg (-1) DDS in dimethylsulfoxide (DMSO) and groups 2-4 received the same treatment as group 1 but after the administration of a single dose of 100, 150 and 200 mg kg (-1) CIM, respectively, injected 2 h prior DDS administration. Groups 5-9 received the same treatment as group 2 but after the treatment of ranitidine (50 and 100 mg kg (-1) intraperitoneally (i.p.) in 200 microl DMSO) and famotidine (10, 50 and 100 mg kg (-1) i.p. in 200 microl DMSO), respectively. The animals were then anaesthetized with ether and blood was collected from the aorta for the determination of plasma DDS and monoacetyldapsone concentrations by HPLC and later for the determination of methaemoglobinaemia by spectrophotometry. CIM showed a higher affinity for cytochrome P-450 than famotidine and ranitidine. The results obtained showed the potentiality of the pharmacological effects of DDS with a low risk of adverse reactions, especially methaemoglobinaemia, which is dose dependent., (Copyright 2002 Elsevier Science Ltd. All rights reserved.)

We investigated the immunohematoxicities of the antiparasitic drug dapsone (DDS) and the antiretroviral drug zidovudine (ZDV, AZT) given alone or in combination in BALB/c mice. DDS is used for prophylaxis and treatment of Pneumocystis carinii infection in AIDS patients. We examined the impact of concurrent administration of these drugs on the immune and hematopoietic systems because DDS causes hematotoxicity and ZDV therapy results in bone marrow toxicity. Daily oral administration of DDS at 25 and 50 mg/kg for 28 days caused a slight anemia, marked methemoglobinemia, reticulocytosis, and a moderate leukopenia (P < 0.01 for all parameters) but had no discernible effect on platelet count. In DDS-treated mice, the proliferative response of splenic T cells to concanavalin A was > or = 35% higher than that manifested by splenocytes from vehicle-treated control mice. ZDV at 240 and 480 mg/kg was not immunosuppressive but caused low-grade macrocytic anemia, thrombocytosis, and neutropenia; these effects were drug dose-dependent and statistically significant (P < 0.01). Concurrent administration of DDS and ZDV augmented the severity of ZDV-mediated macrocytic anemia, and 7 of 12 (58%) mice did not survive treatment with the high doses of DDS and ZDV (50 and 480 mg/kg, respectively). On the other hand, co-administration of ZDV mitigated DDS-induced methemoglobinemia and the DDS-associated elevation in lymphoproliferative response. These data suggest interaction between DDS and ZDV in mice and indicate a need for caution in using DDS as long-term therapy in AIDS patients receiving ZDV.

Pneumocystis carinii pneumonia (PCP) is a life-threatening but preventable infection that may occur after bone marrow transplantation (BMT). Although various prophylactic regimens have been used in this setting to prevent active infection, their efficacy, toxicity profile, and impact on outcomes are poorly described in this patient group. We undertook a retrospective cohort study in which we reviewed the records of 451 adult patients who underwent BMT for hematologic malignancies, aplastic anemia, or myelodysplasia over a 7-year period at the Brigham and Women's Hospital. Post-BMT PCP prophylaxis consisted of aerosolized pentamidine (AP) 150 mg every 2 weeks or 300 mg per month, trimethoprim/sulfamethoxazole (TMP/SMX) 160/800 mg orally b.i.d. 3 times per week, or dapsone 100 mg orally each day. Prophylaxis was continued for 1 year post-BMT in all patients when clinically feasible. One hundred twenty-one patients were unevaluable because of death or relapse <60 days after BMT (n = 89), loss to follow-up upon hospital discharge (n = 20), or other reasons (n = 12). Three eligible patients did not receive any prophylaxis and were not further evaluated. Of the 327 patients analyzed, 133 underwent autologous BMT, 4 syngeneic BMT, 159 related allogeneic BMT, and 31 unrelated allogeneic BMT. Graft-versus-host disease prophylaxis in the 190 patients receiving allogeneic BMT consisted of T-cell depletion with anti-CD5 and complement in 58 patients and cyclosporine/methotrexate or FK506 with or without steroids in 132 patients. Eight of 327 (2.4%) documented PCP cases were identified, 0 of 105 in patients receiving only TMP/SMX. Four cases occurred in patients receiving only AP (4/44, 9.1%; odds ratio [OR] relative to TMP/SMX 23.4, 95% confidence interval [CI] 1.2, 445.2); 1 in patients receiving only dapsone (1/31, 3.2%; OR not significant); 2 in patients receiving more than 1 prophylactic regimen (2/147 1.4%; OR not significant); and 1 >1 year post-BMT in a patient who was off PCP prophylaxis. Although the patients receiving only AP had a significantly lower probability of treatment-related toxicity than those receiving TMP/SMX (OR 0.19 [95% CI 0.04, 0.851), the probability of their acquiring other serious non-PCP infections was increased (OR 2.2 [95% CI 1.0, 4.6]), and the probability of their dying by 1 year post-BMT was significantly higher (OR 5.2 [95% CI 2.4, 26.6]), even when adjusted for variables such as type of BMT (autologous versus allogeneic; high versus low risk) and sex. Although AP is associated with fewer toxicities, the data show that it is inferior to TMP/SMX in preventing PCP in the post-BMT setting and is associated with an increased risk of other infections and a higher mortality at 1 year after BMT.

Incubation of rat erythrocytes with the hydroxylated metabolites of aniline and dapsone (4-4'-diaminodiphenylsulfone), phenylhydroxylamine and dapsone hydroxylamine, respectively, induced marked release of iron and methemoglobin formation. On the contrary, no release of iron nor methemoglobin formation was seen when the erythrocytes were incubated with the parent compounds (aniline and dapsone). The acute intoxication of rats with aniline or dapsone induced a marked increase in the erythrocyte content of free iron and methemoglobin, indicating that the xenobiotics are effective only after biotransformation to toxic metabolites in vivo. Prolonged administration of aniline or dapsone to rats produced continuous release of iron from erythrocytes. Marked iron overload was seen in the spleen and in the liver Kupffer cells, as detected histochemically. The spleen weight in these subchronically treated animals was significantly increased. The free iron pool was markedly increased in the spleen and to a lower extent in the liver. The possible relationships between iron release in erythrocytes, oxidative damage seen in senescent cells, hemolysis, overwhelmed capacity of spleen and liver to keep iron in storage forms and subsequent increase in low molecular weight, catalitically active iron is discussed.

Differences in the incidence of adverse drug reactions to trimethoprim-sulfamethoxazole and dapsone may result from differences in the formation, disposition, toxicity, and/or detoxification of their hydroxylamine metabolites. In this study, we examine whether differences in the biochemical processing of sulfamethoxazole hydroxylamine (SMX-NOH) and dapsone hydroxylamine (DDS-NOH) by erythrocytes [red blood cells (RBCs)] contribute to this differential incidence. The methemoglobin (MetHgb)-forming capacity of both metabolites was compared after a 60-min incubation with washed RBCs from four healthy human volunteers. DDS-NOH was significantly more potent (P =.004) but equally efficacious with SMX-NOH in its ability to form MetHgb. The elimination of potential differences in disposition by lysing RBCs did not change the MetHgb-forming potency of either hydroxylamine. At pharmacologically relevant concentrations, greater reduction to the parent amine occurred with DDS-NOH. Maintenance of MetHgb-forming potency was dependent on recycling with glutathione, but no difference in cycling efficiency was observed between DDS-NOH and SMX-NOH. In contrast, the pharmacodynamics of hydroxylamine-induced MetHgb formation were not changed by pretreatment with the glucose 6-phosphate dehydrogenase inhibitor epiandrosterone or by compounds that alter normal antioxidant enzyme activity. Methylene blue, which stimulates NADPH-dependent MetHgb reductase activity, decreased MetHgb levels but did not alter the differential potency of these hydroxylamines. DDS-NOH was also significantly more potent when incubated with purified human hemoglobin A0. Collectively, these data suggest that the inherently greater reactivity of DDS-NOH with hemoglobin, the greater conversion of DDS-NOH to its parent amine, and potential differences in disposition of hydroxylamine metabolites may contribute to the preferential development of dapsone-induced hemotoxicity and sulfamethoxazole-induced hypersensitivity reactions.

The metabolism and toxicity of dapsone was compared in vitro and in vivo in rat, mouse and man. Metabolism was assessed by high-pressure liquid chromatography-mass spectrometry and methemoglobin formation has been used as a toxic endpoint. The greatest toxicity in vitro was seen in microsomes prepared from male Wistar rats (36.6 +/- 1.5% methemoglobin), although toxicity was also seen in microsomes from the female rat (8.2 +/- 1.3%), male CD1 (4.2 +/- 1.6%) and human (10. 9 +/- 1.1%). The rank order of toxicity agreed with the formation of the hydroxylamine metabolite in vitro. All microsomes were also capable of catalyzing the reverse reaction, i.e., reduction of the hydroxylamine to dapsone. However, in vivo administration of dapsone resulted in significant (P < 0.05) methemoglobinemia only in male rats and humans. This species difference in the susceptibility to dapsone toxicity could not be attributed solely to the sensitivity of the target erythrocytes, because the order of sensitivity to dapsone hydroxylamine was human > mouse > rat. Analysis of bile and urine revealed the formation of dapsone hydroxylamine and its glucuronide in male rats and humans, but not in female rats or mice. This species difference in the metabolism and toxicity of dapsone has important implications in the safety evaluation of related compounds for man.

The structural basis of dapsone (4,4'-diaminodiphenyl sulphone) haemotoxicity has been determined by investigation of the in vitro bioactivation of a series of 4-substituted arylamines. In the presence of rat liver microsomes, dapsone (100 microM) was the most potent former of methaemoglobin in human erythrocytes (44.8 +/- 6.7%). Substitution of the sulphone group with sulphur (11.6 +/- 1.4% methaemoglobin), oxygen (4.5 +/- 1.1%), nitrogen (0.0 +/- 3.2%), carbon (13.6 +/- 0.8%) or a keto group (34.0 +/- 6.1%) resulted in a decrease in methaemoglobin formation. Only one compound, 4,4'-diaminodiphenylamine, generated significant (P < 0.001) amounts of methaemoglobin (25.6 +/- 2.5%) in the absence of NADPH. To assess further the role of the 4-substituent in methaemoglobinaemia, the toxicity of a series of 4-substituted aniline derivatives was also studied. Of the anilines studied, 4-nitroaniline caused the most methaemoglobin (36.5 +/- 8.0%), whilst aniline caused the least (0.3 +/- 0.5%). Overall, there was a significant correlation (r2 = 0.83) between the haemotoxicity and the Hammett constant, sigma(p), suggesting that it is the electron-withdrawing properties of the substituent that influence the methaemoglobin formation. In the presence of microsomes prepared from two human livers, dapsone was the most haemotoxic bis arylamine, whereas 4-iodoaniline was the most potent methaemoglobin former (60.6 and 73.6%) and aniline the least potent (1.1 and 2.4%). As a whole, these results indicate that the sulphonyl group, which is essential for the pharmacological activity of dapsone, is also largely responsible for the haemotoxicity seen with this drug.

The industrial curing agent 4,4'-methylene-bis(2-chloroaniline) (MOCA) and the structurally related medicinal agent 4,4'-sulphonyldianiline (dapsone), are two commonly used aromatic amine compounds and documented animal carcinogens. In this study the effects of in vitro exposure to MOCA and dapsone (over a dose range of 1-200 microM on spleen and liver immune cell functions were investigated. MOCA exposure caused a dose-dependent inhibition of natural immune activities (i.e. natural killer, NK and natural P815 killer, NPK) and mitogen-stimulated proliferation of T- and B-lymphocytes, with 50% inhibition (IC50) of splenic-cell activities occurring at 145, 85, 21 and 31 microM, respectively. Liver NK and NPK activities were less sensitive to MOCA exposure and exhibited higher IC50's of 165 and 160 microM, respectively. Dapsone exposure slightly enhanced both T- and B-cell mitogenesis at low doses (1 microM) but decreased B-cell mitogenesis at high doses (IC50 = 130 microM). Natural tumouricidal activities were generally unaffected by dapsone, whilst natural cytotoxic (NC) activity was unaffected by both compounds. These results indicate that MOCA is generally immunotoxic in vitro, and may have the potential to enhance the carcinogenic effects of its genotoxic metabolite by inhibiting the tumour surveillance activities of the immune system. The relationship between immune effects and the carcinogenicity of dapsone remains unclear.

Three metabolizing systems (rat, heterologously expressed CYP3A4 and human liver) were used to evaluate 12 analogues of dapsone (4,4'diaminodiphenylsulphone) in-vitro. Methaemoglobin formation in a two-compartment and cytotoxicity in a single-compartment model were studied using human erythrocytes and neutrophils, respectively, as target cells. In the two-compartment system using rat microsomes as a generating system and methaemoglobin as an endpoint, the least potent methaemoglobin formers tested were the 2-methyl-4-propylamino (AXDD14), 2-hydroxy-4-4'amino (ABDD5) derivatives and a sulphone/trimethoprim derivative (K-130). Dapsone itself, a 2-methoxy-4-ethylamino (W10) and a 2-hydroxyl-4-ethylamino compound (ABDD39) were the most toxic. In the single-compartment cytotoxicity test using rat microsomes, AXDD14 was again among the least toxic, as was a 2-methyl 4-cyclopentyl derivative (AXDD17) and surprisingly ABDD39. The most cytotoxic compounds again included dapsone itself as well as two 2-trifluoromethyl derivatives. The only significant methaemoglobin formation and cytotoxicity shown with the heterologously expressed human CYP 3A4 was with AXDD14, which was extensively activated. Interestingly, metabolism of dapsone was low using the expressed CYP 3A4. In the two-compartment system using human liver microsomes, AXDD14, K-130 and ABDD5 were oxidized to a significantly lesser extent compared with dapsone and these preliminary findings indicate that future development of these compounds may be worthwhile.

Various quinolones have varied effects on the preservative activity of blood cells. Nalidixic acid causes hemolysis in G-6PD deficient patients where as ofloxacin has been found to possess preservative action of WBCs. The present study was undertaken to see the effect of various fluoroquinolones on RBC membrane. The effect of quinolones like ciprofloxacin, ofloxacin and norfloxacin and nalidixic acid in the dose of 5 micrograms/ml was studied on dapsone induced, in vitro hemolysis of rabbit RBC, using the osmotic fragility test. The mean corpusular fragility (MCF) with various agents were as follows: (mean +/- SE) saline; 5.23 +/- 0.21; dapsone, 6.57 +/- 0.23; ofloxacin, 3.81 +/- 0.13; ofloxacin and dapsone, 5.13 +/- 0.11; nalidixic acid, 6.28 +/- 0.16; nalidixic acid and dapsone, 6.65 +/- 0.13; ciprofloxacin, 3.52 +/- 0.22; ciprofloxacin and dapsone, 4.80 +/- 0.2; norfloxacin, 1.97 +/- 0.23; norfloxacin and dapsone, 4.27 +/- 0.20. The MCF data and shift of the osmotic fragility curves (to the left) show that dapsone induced erythrolysis is significantly protected by ciprofloxacin, ofloxacin and norfloxacin but not by nalidixic acid.

Dapsone hydroxylamine is a direct-acting hemolytic agent responsible for dapsone-induced hemolytic anemia in the rat. In the present study, we compared the responsiveness of rat and human red cells to dapsone hydroxylamine-induced cellular changes. Dapsone hydroxylamine induced a rapid and concentration-dependent loss of erythrocytic reduced glutathione content with a concomitant increase in protein-glutathione mixed disulfide formation in both human and rat red cell suspensions. However, the rate of mixed disulfide formation in human cells was considerably slower than that in rat cells and was preceded by a transient increase in oxidized glutathione (glutathione disulfide) formation. Sodium dodecylsulfate-polyacrylamide gel electrophoresis and immunoblotting analysis of membrane ghosts from human red cells revealed changes in skeletal proteins that in general were similar to those observed with rat cells, including a loss of protein band 2.1 and the appearance of membrane-bound hemoglobin. Notable differences were the resistance to loss of band 4.2 and a considerably higher amount of protein aggregation in human ghosts. Although the morphology of human red cells was altered, the incidence and degree of change were considerably less than those of rat red cells. Furthermore, the concentration of dapsone hydroxylamine required to induce damage in human red cells (175-750 microM) was significantly higher than that required for rat red cells (50-175 microM), suggesting that human cells are probably less sensitive than rat cells to dapsone hydroxylamine-induced oxidative damage.

Individuals deficient in erythrocytic glucose-6-phosphate dehydrogenase (G6PD) show about a 2-fold increase in sensitivity toward dapsone-induced hemolytic anemia. Rat studies have shown that the hemolytic activity of dapsone resides in its N-hydroxy metabolites; exposure of rat red cells to N-hydroxy-dapsone in vitro followed by readministration to isologous rats results in premature splenic sequestration of the damaged cells. This study examines the ability of the steroid, epiandrosterone, to inhibit rat red cell G6PD and the effect of such inhibition on the susceptibility of rat red cells to N-hydroxydapsone hemolytic activity. Epiandrosterone was found to inhibit rat red cell G6PD uncompetitively and to suppress red cell hexose monophosphate shunt activity by more than 95%. Epiandrosterone suppression of rat red cell G6PD activity resulted in about a 2-fold increase in sensitivity of the rat cells to N-hydroxydapsone hemolytic activity, and a modest but significant increase in depletion of red cell glutathione. In contrast, suppression of rat red cell catalase activity by aminotriazole had no effect on the hemotoxicity of N-hydroxydapsone. Epiandrosterone appears to be a useful tool to explore the mechanism by which G6PD deficiency enhances susceptibility to hemolytic drugs.

Dapsone, an old drug introduced and used almost exclusively for the treatment of leprosy, is now utilized in an increasing number of therapeutic situations. However, its hemotoxicity is potentially severe and is often dose limiting. Effective countermeasures, based on resolution of the mechanisms underlying dapsone-induced hemotoxicity, could significantly enhance the therapeutic value of the drug. In studies on rat red cells, we have established that the N-hydroxy metabolites of dapsone, DDS-NOH and MADDS-NOH, are direct-acting hemolytic agents, that they are formed in amounts sufficient to account for the hemotoxicity of the parent drug, and that the action of these toxic metabolites in the red cell induces premature sequestration by the spleen. Incubation of rat red cells with hemolytic concentrations of arylhydroxylamines leads to the generation of hydroxyl, glutathiyl, and hemoglobinthiyl radicals, and the formation of protein-glutathione mixed disulfides. Disulfide-linked adducts are also formed between membrane skeletal proteins and hemoglobin monomers, as well as between the monomeric hemoglobin units forming dimers, trimers, tetramers, and pentamers. Profound morphological changes are seen with change from normal discoidocity to an extreme nonspherocytic enchinocyte shape. Parallel studies with human red cells indicate that the response of human cells is qualitatively similar but that there are notable differences in regard to skeletal membrane effects. A working hypothesis for the mechanism underlying dapsone hemolytic activity is proposed.

The relative methemoglobin (MetHgb) forming ability of two metabolites of dapsone, dapsone hydroxylamine (DDS-NOH) and monoacetyldapsone hydroxylamine (MADDS-NOH), were compared in rat and human whole blood. Concentration-response curves for the two metabolites were generated in vitro in whole blood. Data were fit to both the Emax and Sigmoid Emax models. The Emax values for MetHgb formation in rat blood for MADDS-NOH and DDS-NOH fitted to the Emax model were 83 (8) and 84 (2)%, while the EC50 values were 1087 (283) and 828 (104) microM, respectively (mean +/- SD). Neither these values nor those generated for the Sigmoid Emax model differed significantly between the two metabolites. Similarly, the Emax values in human blood for MADDS-NOH and DDS-NOH fitted to the Emax model were 79 (5) and 80 (2)%, while the EC50 values were 90 (17) and 95 (19) microM, respectively. These values also did not differ between the two metabolites using either pharmacodynamic model. MetHgb was produced at the same rate, reached similar peak concentrations, and exhibited the same rate of decline with both metabolites. The area under the MetHgb content versus time curve did not differ between the two metabolites. These data demonstrate that MADDS-NOH and DDS-NOH are equipotent and equally efficacious in their MetHgb-forming ability. Investigation of the disposition of these metabolites is necessary to assess their relative role in dapsone-induced toxicity in vivo.

1. N-hydroxylation is thought to be an essential step in the haemotoxicity of dapsone (DDS). To investigate both metabolism-dependent and cell-selective drug toxicity in vitro we have developed a three-compartment system in which an hepatic drug metabolizing system is contained within a central compartment separated by semipermeable membranes from compartments containing mononuclear leucocytes (MNL) and red blood cells (RBC). 2. Metabolism of dapsone (100 microM) by rat liver microsomes resulted in toxicity to RBC cells (47.3 +/- 2.1% methaemoglobin), but there was no significant toxicity toward MNL (3.7 +/- 1.3% cell death) compared with control values (1.6 +/- 0.9%). However, when RBC were replaced with buffer in the third compartment there was significantly greater (P < 0.001) white cell toxicity (17.6 +/- 0.6% cell death), demonstrating the protection of MNL by RBC. Metabolism of dapsone by human liver microsomes again resulted in RBC toxicity (12.5 +/- 3.3% methaemoglobin) but no significant MNL toxicity (2.9 +/- 0.8% cell death). Replacement of RBC resulted in a significant (P < 0.001) increase in MNL toxicity (6.5 +/- 0.7% cell death). Addition of synthetic dapsone hydroxylamine (30 microM) in the absence of a metabolizing system and with no RBC in the third compartment resulted in significant (P < 0.001) toxicity toward MNL (43.36 +/- 5.82% cell death) compared with control (1.8 +/- 1.1%). The presence of RBC in the third compartment resulted in a significant (P < 0.001) decrease in MNL toxicity (17.6 +/- 2.2% cell death), with 40.1 +/- 3.7% methaemoglobin in the RBC.(ABSTRACT TRUNCATED AT 250 WORDS)

In MRC-5 cell cultures, the efficacy of the acyclic nucleoside ganciclovir (GCV) against human cytomegalovirus (CMV) was unaffected when combined with either amphotericin B (AMP B), ketoconazole (KCZ), dapsone (DAP), or trimethoprim/sulfamethoxazole (TMP/SMX). When differences in 3-dimensional plots for antiviral activity and cytotoxicity of GCV alone and in combination were compared, the anti-CMV activity of GCV (IC50 8 microM, 5-9 microM range) was not affected by concentrations of up to 10 microM AMP B, 1000 microM KCZ, 100 microM DAP or 320 microM TMP/SMX (higher concentrations could not be tested due to cytotoxicity). In Swiss Webster mice, the anti-CMV activity of GCV was also unaffected when administered in combination with any of the four other antimicrobial agents against murine CMV. GCV (s.c.) alone had an ED50 of 7 mg/kg (2-12 mg/kg range) which was unaffected by daily doses of 1 mg/kg AMP B (i.p.), 60 mg/kg KCZ (i.p.), 32 mg/kg DAP (p.o.) or 80/400 mg/kg TMP/SMX (p.o.). These results suggest that GCV can be administered in combination with these other drugs for treatment of various opportunistic infections in AIDS patients without compromising the efficacy of GCV against CMV.

Dapsone hydroxylamine (DDS-NOH), a known metabolite of dapsone, has recently been shown to be a direct-acting hemotoxin responsible in part for dapsone-induced hemolytic anemia in the rat. The effect of DDS-NOH on the morphology, sulfhydryl status, and membrane skeletal proteins of the rat red cell has been investigated. Exposure of rat red cells to a TC50 of DDS-NOH induced transformation of about 50% of the cells to an extreme echinocyte morphology. Reduced glutathione content of the cells was rapidly lost with concomitant increase in the formation of mixed disulfide between glutathione and the soluble protein of the cell. Oxidized glutathione content of the cells did not increase at any time during exposure to DDS-NOH. Examination of the skeletal membrane proteins by SDS-PAGE indicated that DDS-NOH caused the apparent loss of band 4.2, decrease in peaks 1, 2.1, and 3, and the appearance of new bands at about 16, 27, 40, and 54 kDa. Bands 4.1 and 7 appeared unchanged. Treatment of DDS-NOH altered proteins with dithiothreitol, reversed the protein changes, and indicated that the observed alterations were due to the formation of disulfide-linked adducts between hemoglobin and the various skeletal proteins as well as between hemoglobin monomers. The possible significance of the parallel changes in cell morphology and in membrane skeletal proteins for the premature splenic sequestration of the injured rat red cells is discussed.

Objective: To compare the haematological toxicity and efficacy of oral dapsone and nebulized pentamidine as Pneumocystis carinii pneumonia (PCP) prophylaxis in HIV-infected patients receiving zidovudine., Design: Randomized, prospective., Setting: Infectious diseases hospital with participants drawn from both inpatient and outpatient departments., Patients: Those eligible were starting treatment with zidovudine, needed PCP prophylaxis (CD4+ count < 200 x 10(6)/l or < 20% total lymphocyte count or previous episode of PCP), and had a normal glucose-6-phosphate dehydrogenase screen. Of the 98 patients enrolled, 96 returned for follow-up., Interventions: Fifty patients received dapsone (100mg orally twice weekly) and 46 pentamidine (400 mg nebulized monthly). Follow-up was for a median of 18 months., Main Outcome Measures: The development of PCP, transfusion requirements, monthly complete blood cell counts, serious adverse reactions and death were recorded., Results: Nine (18%) dapsone and eight (17%) pentamidine recipients developed PCP. There was no significant difference in number of patients transfused (12 dapsone and nine pentamidine recipients) or transfusion-free survival. At exit from the study, mean haemoglobin (11.7 versus 12.4 g/dl), white blood cell (3.9 versus 3.7 x 10(9)/l) and platelet (195 versus 184 x 10(9)/l) counts did not differ for the dapsone and pentamidine arms, respectively. There was no significant difference in the occurrence of serious adverse reactions (six in the dapsone and eight in the pentamidine arm)., Conclusions: Dapsone can be recommended in preference to pentamidine as PCP prophylaxis on the basis of equivalent efficacy, absence of excessive haematological toxicity, low cost and ease of administration.

Administration of dapsone in combination with trimethoprim and cimetidine to male rats resulted in a marked decrease (P less than 0.05) in measured methaemoglobin levels (46.2 +/- 24% Met Hb h) compared with administration of dapsone alone (124.5 +/- 24.4% Met Hb h). The elimination half-life of dapsone (814 +/- 351 min) was more than doubled in the presence of trimethoprim and cimetidine compared with control (355 +/- 160 min, P less than 0.05). However, there were no significant differences in AUC and clearance when dapsone was administered in combination with trimethoprim and cimetidine compared with dapsone alone. Co-administration of trimethoprim with dapsone in the absence of cimetidine did not affect either methaemoglobin formation, AUCs, half-lives, or clearance values of dapsone compared with control. There was a threefold increase in the AUC of trimethoprim (6296 +/- 2249 micrograms min mL-1) in the presence of dapsone compared with trimethoprim alone (2122 +/- 552 micrograms min mL-1). There was also a corresponding decrease in the clearance of trimethoprim in the presence of dapsone compared with control (19.1 +/- 6.9 vs 60.8 +/- 21.0 mL min-1). However, there was no change in the elimination half-life of trimethoprim between the two experimental groups (273 +/- 120 vs 292 +/- 54 min). The AUC of trimethoprim increased more than threefold in the presence of cimetidine (7100 +/- 1501 micrograms min mL-1) compared with trimethoprim alone (2122 +/- 552 micrograms min mL-1).(ABSTRACT TRUNCATED AT 250 WORDS)

With microsomes prepared from a single human liver, 4,4'-diaminodiphenyl sulphone (DDS), 4-acetyl-4-aminodiphenyl sulphone (MADDS), 4-acetyl-4-aminodiphenyl thioether (MADDT) and 4,4'-diacetyldiphenyl thioether (DADDT) caused significantly greater methaemoglobin formation compared with control. In-vitro in the rat, the pattern of toxicity was slightly different:DADDT was not haemotoxic, whilst 3,4'-diaminodiphenyl sulphone (3,4'DDS) and 3,3'-diaminodiphenyl sulphone (3,3'DDS) as well as DDS, MADDS and MADDT were significantly greater than control. 4,4' Acetyl diphenyl sulphone (DADDS), 4,4' diaminodiphenyl thioether (DDT), 4,4'-diaminodiphenyl ether (DDE) and 4,4' diaminooctofluorodiphenyl sulphone (F8DDS) did not cause significant methaemoglobinaemia in either human or rat liver microsomes. DDS, MADDS, and MADDT were not significantly different in haemotoxicity generation in-vitro in the presence of human microsomes. In the rat in-vitro, DDS, MADDS, and 3,4'DDS did not differ significantly in red cell toxicity, and were the most potent methaemoglobin formers. The 3,3'DDS and MADDT derivatives were both significantly less toxic compared with DDS. None of the compounds tested caused haemoglobin oxidation in the absence of NADPH in-vitro. In the whole rat, DDS, MADDS and MADDT caused significantly higher levels of methaemoglobin compared with control. None of the remaining compounds caused methaemoglobin formation which was significantly greater than control. DDS and MADDS were the most potent methaemoglobin formers tested, in-vivo and in-vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Dapsone (4,4'-diaminodiphenyl sulfone; DDS), an established anti-leprosy drug, showed anticonvulsive effects in the amygdaloid kindling model of epilepsy. Single doses of the drug in rats (6.25-12.5 mg/kg, i.p.) suppressed the kindled seizures in a dose-dependent manner without overt behavioral toxicity. With repeated oral administration in cats, relatively higher initial doses (13-23 mg/kg) were required to obtain seizure suppression, and neurotoxic signs occurred within a few days with serum drug levels of approximately 20 micrograms/ml. Although dapsone showed anticonvulsive effects in both animal species, the effective serum levels overlapped the toxic levels reported in the clinical treatment of leprosy. In the majority of the cats, however, seizure suppression was maintained even after the discontinuation of dapsone with lower serum levels than those observed at the beginning of the seizure suppression. Therefore, dapsone would be useful as an antiepileptic drug only when long-term anticonvulsive efficacy is demonstrated using smaller doses comparable to those used in the treatment of leprosy.

Dapsone undergoes N-acetylation to monoacetyl dapsone as well as N-hydroxylation to a hydroxylamine which is responsible for the haemotoxicity (i.e. methaemoglobinaemia; Met Hb) of the drug. Since dapsone is always given chronically, we have investigated the ability of cimetidine to inhibit Met Hb formation caused by repeated dapsone administration. The drug was given (i.p.) to four groups (n = 6 per group) of male Wistar rats, 300-360 g. Group I received 10 mg kg-1 at 1, 24, 48 and 72 h. Group II received 10 mg kg-1 at 1, 8, 24, 32, 48, 56, 72 and 80 h. Groups III and IV received the drug as for groups I and II, respectively, as well as cimetidine (50 mg kg-1) 1 h before each dose of dapsone. Twice daily dapsone administration (Group II) resulted in a significantly greater (P less than 0.05) Met Hb AUC (757 +/- 135 vs 584 +/- 115% Met Hb h), dapsone AUC (140 +/- 17.5 vs 113 +/- 13.0 micrograms h mL-1) and monoacetyl dapsone AUC (48.2 +/- 18.3 vs 10.8 +/- 4.6 micrograms h mL-1) compared with a single daily dapsone dose (group I). The administration of cimetidine before the once daily dose of dapsone (group III) resulted in a significant (P less than 0.05) fall in Met Hb (302 +/- 179 vs 584 +/- 115% Met Hb h) and an increase in both the dapsone (151 +/- 22.2 vs 113 +/- 13.0 micrograms h mL-1) and monoacetyl dapsone AUC values (33.6 +/- 5.8 vs 10.8 +/- 4.0 micrograms h mL-1) compared with a single daily dose of dapsone (group I).(ABSTRACT TRUNCATED AT 250 WORDS)

1. We have utilized a two compartment system in which two teflon chambers are separated by a semi-permeable membrane in order to investigate the role of metabolism in dapsone-induced methaemoglobinaemia. Compartment A contained a drug metabolizing system (microsomes prepared from human liver +/- NADPH), whilst compartment B contained target cells (human red cells). 2. Incubation of dapsone (1-100 microM) with human liver microsomes (2 mg protein) and NADPH (1 mM) in compartment A (final volume 500 microliters) led to a concentration-dependent increase in the methaemoglobinaemia (15.4-18.9% at 100 microM) compared with control (2.3 +/- 0.4%) detected in the red cells within compartment B. In the absence of NADPH dapsone had no effect. 3. Of the putative dapsone metabolites investigated, only dapsone-hydroxylamine caused methaemoglobin formation in the absence of NADPH (40.6 +/- 6.3% with 100 microM). However, methaemoglobin was also detected when monoacetyl-dapsone, 4-amino-4'-nitro-diphenylsulphone and 4-aminoacetyl-4'-nitro-diphenylsulphone were incubated with human liver microsomes in the presence of NADPH. 4 Dapsone-dependent methaemoglobin formation was inhibited by addition of ketoconazole (1-1000 microM) to compartment A, with IC50 values of 285 and 806 microM for the two liver microsomal samples studied. In contrast, methaemoglobin formation was not inhibited by cimetidine or a number of drugs pharmacologically-related to dapsone. The presence of glutathione or ascorbate (500 microM) did not alter the level of methaemoglobin observed.

Administration of dapsone (33 mg kg-1) to intact rats resulted in a marked elevation of methaemoglobin levels in male (435.0 +/- 105.2% met Hb h) compared with female rats (59.0 +/- 17.2% met Hb h). However, the clearance of dapsone was significantly faster in males compared with females. Female rats showed very low levels of methaemoglobin which were accompanied by significantly higher blood concentrations of parent drug. Clearance of dapsone in castrated animals was less than one-third of that of the intact sham-operated males (252.2 +/- 67.2 vs 81.4 +/- 33.0 mL h-1). Likewise, clearance of dapsone in ovarectomized rats was approximately half that of intact females. There were no significant differences in the disposition of dapsone between the ovarectomized (AUC 431.0 +/- 31.7 micrograms h mL-1; t1/2, 15.62 +/- 1.8 h) and castrated (AUC, 450.6 +/- 150.9 micrograms h mL-1; t1/2, 17.6 +/- 7.9 h) animals. However, methaemoglobin levels in castrated males, although less than a third of those of intact males, significantly exceeded those of ovarectomized animals. There was no significant difference between the four groups of animals with respect to red cell sensitivity to the methaemoglobin-forming capacity of the toxic metabolite of dapsone, the hydroxylamine. Metabolic conversion of dapsone to the hydroxylamine in the presence of NADPH was 7.6 +/- 1.5% for liver microsomes from intact males and was significantly greater (P less than 0.05) than the corresponding values for liver microsomes from castrated rats (5.3 +/- 0.59%). Conversion of dapsone to dapsone-NOH by liver microsomes from intact females and ovarectomized animals was below 1% in both cases.(ABSTRACT TRUNCATED AT 250 WORDS)

1. A two compartment system, comprising two adjacent teflon chambers separated by a semi-permeable membrane, has been devised with which to investigate the generation of drug metabolites that are toxic to human cells in vitro. 2. Compartment A contained a drug-metabolising system (human liver microsomes +/- NADPH) and compartment B contained target cells (human mononuclear leucocytes). The semi-permeable membrane retained protein (m.w. greater than 10,000) but allowed equilibration (within 1 h) of drug and drug metabolites, during which time cells remained viable. 3. Incubation of dapsone (100 microM) with human microsomal protein (2 mg ml-1) and NADPH (1 mM) in compartment A caused cell death (8.7 +/- 1.8%) in compartment B, which was reduced significantly (P less than 0.05) by the addition of glutathione (500 microM). Dapsone in the absence of NADPH was not cytotoxic. 4. Chemical analysis showed the presence of dapsone hydroxylamine as the only stable metabolite in both compartment A (5.2 +/- 0.4% incubated drug) and compartment B (3.5 +/- 0.5%). 5. Irreversible binding of dapsone to cells was significantly (P less than 0.05) reduced by omission of NADPH (85 +/- 13 pmol/10(6) cells) or addition of glutathione (103 +/- 9) compared with control values (153 +/- 51).

The effect of 4,4'-methylene bis (2-chloroaniline) (MOCA), 4,4'-methylene dianiline (MDA) and 4,4'-sulfonyl dianiline (Dapsone) on xenobiotic biotransformation in vivo was studied in male rat liver. Treatment with MOCA and MDA caused a dose dependent increase in ethoxyresorufin O-deethylase activity and concomitant decrease in aldrin epoxidase activity. Treatment with MOCA and MDA also resulted in increases in ethoxycoumarin O-deethylation and epoxide hydrolation while only MOCA induced cytosolic glutathione S-transferase activity. Treatment with Dapsone resulted in no changes in xenobiotic biotransformation except for the induction of aniline hydroxylation. The results are consistent with the contention that there is a relationship between carcinogenic chemicals and particular alteration in the activities of biotransformation enzymes.

In six carcinogenicity bioassays, male and female F344 rats were fed diets containing aniline hydrochloride (CAS: 142-04-1; hydrochloride benzenamide), p-chloroaniline (CAS: 106-47-8), azobenzene (CAS: 103-33-3), o-toluidine hydrochloride (CAS: 636-21-5), dapsone (CAS: 80-08-0; 4,4'-sulfonyldianiline), or D & C red No. 9 [CAS: D85500000; 5-chloro-2-[2-hydroxy-1-naphthalenyl)azo)-4-methylbenzenesulfon ic acid, barium salt]. The rats, from 6 weeks to 2 years old, were given the compounds at two dose levels, the estimated maximum tolerated dose and one-half that dose. In all six bioassays, dose-dependent incidences of splenic sarcomas and fibrosis were seen, with the highest incidences in male rats. Fibrosis occurred in the splenic parenchyma and/or the capsule. Fatty infiltration also was seen in the spleen. Sarcomas appeared to arise in the splenic red pulp or splenic capsule, usually in association with areas of parenchymal and capsular fibrosis and pigmentation. Larger tumors metastasized to the peritoneal cavity and abdominal organs. In some rats there was marked osseous metaplasia when the primary tumor metastasized to peritoneal surfaces. Other, less common, splenic neoplasms included hemangiosarcoma and hemangiopericytoma. Some rats had such extensive peritoneal involvement that the site of origin of their sarcoma was difficult to determine.