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The clinical utility of therapeutic drug monitoring in tuberculosis has not been adequately evaluated by controlled clinical trials. To examine the relationship between slow culture conversion and peak plasma rifampicin level (Cmax-rfm) in a case-control study, patients with persistence of positive sputum smear despite at least 8 weeks of directly observed treatment with standard pyrazinamide-containing regimens were enrolled prospectively in government chest clinics from 16 December 2005 to 15 November 2006. Patients with multidrug-resistant tuberculosis, human immunodeficiency virus infection, or poor treatment adherence were excluded. Cases referred to patients with persistence of positive culture whereas controls had negative culture despite positive smear. Blood was checked at 2 and 4 hours post-dosing to capture Cmax-rfm. A cohort of 88 patients was identified. After excluding 16 patients, there were 36 controls and 36 cases. None had symptoms of malabsorption. Cmax-rfm was below 6 mg/l among 47% of controls and 44% of cases. Univariate and multiple logistic regression analyses showed no significant association between slow culture conversion and Cmax-rfm after logarithmic transformation. Thus, there is probably no association between Cmax-rfm and slow culture conversion.

Objective: Previous research in healthy volunteers has demonstrated that rifampicin and adjusted doses of lopinavir/ritonavir soft-gel capsules resulted in adequate exposure to lopinavir. Our objective was to study the combined use of rifampicin and the newly introduced lopinavir/ritonavir tablets., Methods: A total of 40 healthy volunteers were planned to start with 600 mg rifampicin once daily from days 1-5. From days 6-15, volunteers were randomized to receive lopinavir/ritonavir tablets dosed as either 600/150 or 800/200 mg twice daily, both in addition to 600 mg rifampicin once daily. A 12 h pharmacokinetic curve was planned on day 15. Safety assessments were conducted regularly throughout the study period., Results: Eleven volunteers started as the first group in this study. No major complaints occurred during day 1-5 (rifampicin only). After addition of lopinavir/ritonavir, eight volunteers suffered from both nausea and vomiting, one from nausea only, and one from vomiting only. On day 7, increases in aspartate aminotransferase/alanine aminotransferase (AST/ALT) levels were reported in all volunteers and on day 8, the study was prematurely terminated. The AST/ALT levels continued to rise and peaked (grade 2, n = 2; grade 3, n = 1; grade 4, n = 8) on days 9-10. All values returned to normal within 6 weeks., Conclusions: The study showed a high incidence of adverse events when a higher than standard dose of the new lopinavir/ritonavir tablets was combined with rifampicin. In the future, this drug combination should not be given to healthy volunteers. Liver function should be carefully monitored when rifampicin and lopinavir/ritonavir are combined in patients.

A high performance liquid chromatographic (HPLC) method for the determination of imipenem and rifampicin was developed and validated. The method involves plasma deproteinisation with methanol, gradient elution on a RP-18 column and diode array detection. Separation was carried out in 8 min using a mobile phase composed of methanol and 0.2M borate buffer (pH 7.2). Imipenem and rifampicin were detected at 300 nm and 255 nm, respectively. A linear response was observed at plasma levels ranged between 0.3 and 30 microgmL(-1) for imipenem and 1.5 and 20 microgmL(-1) for rifampicin. The detection limits were 0.07 microgmL(-1) and 0.47 microgmL(-1) for imipenem and rifampicin, respectively. The method was applied to the determination of both compounds in mouse plasma samples.

Background and Objectives: Nevirapine-containing antiretroviral therapy (ART) and rifampicin-based antitubercular therapy are commonly co-administered in Africa, where nevirapine is often the only available non-nucleoside reverse transcriptase inhibitor. Rifampicin induces the metabolism of nevirapine, but the extent of the reduction in nevirapine concentrations has varied widely in previous studies. We describe the steady-state pharmacokinetics of nevirapine during and after antitubercular therapy in South African patients., Methods: Sixteen patients receiving ART including standard doses of nevirapine were admitted twice for intensive pharmacokinetic sampling: during and after rifampicin-based antitubercular therapy., Results: Geometric mean ratios for nevirapine pharmacokinetic parameters during versus after antitubercular therapy were 0.61 [90% confidence interval (CI) 0.49-0.79] for Cmax, 0.64 (90% CI 0.52-0.80) for area under the curve up to 12 h (AUC(0-12)) and 0.68 (90% CI 0.53-0.86) for Cmin. Nevirapine Cmin was subtherapeutic (<3 mg/L) in six patients during antitubercular therapy (one of whom developed virological failure) and in none afterwards. There was no correlation between rifampicin concentrations and the degree of nevirapine induction assessed by the proportional change in nevirapine concentrations between the two admissions. The ratio of nevirapine AUC(0-12) to the AUC(0-12) of its 12-hydroxy metabolite was significantly lower in the presence of antitubercular therapy, consistent with induced metabolism., Conclusions: Nevirapine concentrations were significantly decreased by concomitant rifampicin-based antitubercular therapy and a high proportion of patients had subtherapeutic plasma concentrations. Further study in African patients is required to determine the implications for treatment outcomes.

Simple and rapid reversed-phase high-performance liquid chromatographic assays with ultraviolet detection have been developed and validated for the determination of amoxicillin, flucloxacillin and rifampicin in neonatal plasma. Plasma samples were either precipitated with perchloric acid (amoxicillin) or methanol (rifampicin) or extracted with methylene chloride (flucloxacillin). Precision coefficients of variation and inaccuracy were less than 15% for all three assays. Only small sample volumes (20-40 microL) were required, making the assays suitable for therapeutic drug monitoring and pharmacokinetic studies in preterm and term neonates. The assays have successfully been applied to analysis of amoxicillin, flucloxacillin and rifampicin in previously published pharmacokinetic studies in neonates.

Factors that relate to medium-term outcome in patients with pulmonary tuberculosis (PTB) who have completed the 2-month intensive phase of treatment are incompletely understood. The relationship between in vitro production of interferon-gamma (IFN-gamma), interleukins (ILs)-5 and -10 and drug levels determined after 2 months of drug therapy, to outcome at 24 months was studied prospectively. Cytokine concentrations were determined from culture supernatants after stimulation of whole blood with purified protein derivative (PPD) of Mycobacterium tuberculosis. Plasma concentrations of rifampin, isoniazid, pyrazinamide and ethambutol were determined by high-performance liquid chromatography. The treatment failure and relapse free survival probability was 0.54 (95% CI: 0.40-0.67) at 24 months. In multivariate analysis of parameters at 2 months the strongest positive associations with disease free survival were IFN-gamma response to PPD (p=0.002) and serum creatinine (p=0.001). Drug concentrations were not associated with outcome although rifampin exposure correlated with IFN-gamma response to PPD (p=0.0132). These data suggest that the ability to mount a recall immune response to M. tuberculosis may influence treatment outcome. The data support the idea to identify persons at risk of a poor treatment outcome by monitoring of the in vitro response to tuberculosis antigens.

Rifampicin is active against both intracellular and extracellular Mycobacterium tuberculosis. The ability to measure rifampicin drug concentrations in both plasma and in cells may be useful in evaluating the suitability of dosage regimens for populations and individuals. Here a novel simple, precise and accurate method for the quantification of rifampicin in both cells and plasma is reported. Sample proteins were precipitated with acetonitrile containing the internal standard and then diluted with water. Aliquots of supernatant were then injected into the HPLC-MS system for chromatographic separation and detection. Rifampicin calibration curves encompassed concentrations from 100 to 12,800 ng/mL. Intra- and inter-assay precision and accuracy were determined using low, medium and high concentration quality control samples and was found to be within 10% in all cases. Rifampicin concentrations were found to be unaffected by freeze-thaw cycles, but were significantly affected by heat-inactivation (58 degrees C, 40 min). This assay was successfully utilised to determine the pharmacokinetic profile of rifampicin in plasma and peripheral blood mononuclear cells (PBMC) in 8 tuberculosis patients receiving rifampicin over an 8h period.

Despite refinements in surgical techniques, routine antibioprophylaxis, and anesthesiology, vascular prosthetic infections remain a serious complication of reconstructive vascular surgery. The purpose of this study was to evaluate the healing, the toxicity, and the antibiotic delivery of a new vascular graft, preloaded with rifampin and tobramycin. Sixteen dogs underwent infrarenal aortic bypass. They were divided into three groups. In test group 1 (n = 8), dogs received grafts loaded with a standard concentration of antibiotics. In test group 2 (n = 4), dogs received grafts loaded with twice the standard concentration of antibiotics. A control group (n = 4) received a commercial gelatin-sealed graft. Grafts were harvested after different periods of time and submitted to histological evaluation and antibiotic dose determination. Liver and kidney toxicities were evaluated from dosages performed on serum samples taken at different time periods between graft implantation and harvesting. The healing of antibiotic-loaded grafts was similar to that of commercial grafts, without any signs of toxicity. These results suggest resistance to infection of these prebonded grafts in an animal model.

Setting: Low serum concentrations of anti-tuberculosis drugs have occasionally been associated with treatment failure., Objective: To determine the prevalence of low serum concentrations of anti-tuberculosis drugs and to identify the determinants of drug concentrations., Design: Venous blood was obtained 2 h after drug ingestion, and serum levels of isoniazid (INH), rifampicin (RMP), ethambutol (EMB), pyrazinamide (PZA), acetyl INH and 25-desacetyl RMP were analysed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Patients with human immunodeficiency virus co-infection and gastrointestinal disease or diarrhoea were excluded., Results: Among 69 enrolled TB patients, the prevalence of a low 2 h serum concentration of at least one anti-tuberculosis drug was 46.4%. Prevalences of a low concentration of INH, RMP, EMB or PZA were 15.2%, 23.5%, 22.4% and 4.5%, respectively. By multivariate linear regression analysis, the serum concentrations of INH, RMP and PZA were positively associated with dose per kg of body weight (P < 0.05). Moreover, INH concentration was associated with acetyl INH/INH ratio (beta = -8.588, P < 0.001) and EMB concentration was associated with calculated creatinine clearance (beta = -0.025, P < 0.001)., Conclusion: Low concentrations of anti-tuberculosis drugs are common, and although the clinical significance of low concentrations remains uncertain, it may be necessary to optimise drug doses by therapeutic drug monitoring, especially in patients with an inadequate clinical response to chemotherapy.

A high performance liquid chromatography method has been developed that allows quantification of concentrations of rifampicin in human plasma and blood spots. Rifampicin and papaverine hydrochloride (internal standard) were extracted from plasma using a Strata-X-CW extraction cartridge. These analytes were also extracted into acetonitrile from blood spots dried onto a specimen collection card. The recovery of rifampicin from plasma and blood spots was 84.5% and 65.0%, respectively. Separation was achieved by HPLC on a Kromasil C(18) column with a mobile phase composed of ammonium acetate (20 mM, pH 4.0) and acetonitrile, delivered on a gradient programme. Optimum detection was at 334 nm. The assay was linear over the concentration range of 0.5-20 microg/ml. The limit of quantification was 0.5 microg/ml in plasma; 1.5 microg/ml in blood spots. Both intraday and interday precision data showed reproducibility (R.S.D.< or =8.0, n=9). Stability studies showed rifampicin was stable in plasma for up to 9h after thawing; the samples were also stable for up to 9h after preparation. Five patient samples were analysed using the methods described. A correlation was found between the concentrations of RIF in plasma and blood spots (r(2)=0.92). This method is proposed as a means of therapeutic drug monitoring of rifampicin in patients with tuberculosis.

Purpose: We reviewed the interaction between rifampicin (RFP) and clarithromycin (CAM) during treatment of pulmonary Mycobacterium avium complex infection., Subjects and Methods: The subjects were patients with pulmonary non-tuberculous acid-fast bacillus infection during the period from September 2004 to January 2006 who consented to this study. Drug blood concentrations were compared with the minimum inhibitory concentrations for M. avium isolated from sputum and blood levels of CAM were assessed when the time of administration was changed for RFP., Results: The blood concentration of CAM showed a marked decrease in all cases (n = 6) when administered together with RFP, but there was no significant difference in the blood concentration of 14-R-hydroxy-clarithromycin (M-5), the active metabolite of CAM. However, the total blood concentration of CAM and M-5 showed a significant fall, similar to the blood concentration of CAM alone. When the blood concentration and bacterial MIC were compared for RFP, the blood concentration exceeded five MIC(s) in six samples as did the CAM+M-5 level in four out of six samples. There was no significant difference in the blood concentration of CAM (n = 5) when the time of RFP administration was altered. CONCLUSION; Because the total blood concentration of CAM+M-5 fell markedly by co-administration of RFP, this might have an influence on the antibacterial effect of CAM. In addition, examination of the administration of RFP and CAM at different times showed that the blood concentration of CAM did not increase and the influence of induction of hepatic drug-metabolizing enzymes by RFP could not be avoided.

The aim of this study was to assess the frequency of gastrointestinal side effects (GSE) and hepatotoxicity in patients treated with rifampicin for an osteoarticular infection and to determine if there is an association between rifampicin plasma concentrations and side effects. Rifampicin plasma concentrations were prospectively measured before (trough concentration, C(0)) and 2 +/- 0.5 h (peak concentration, C(2)) after drug intake. The presence of GSE, the alanine transferase (ALT) value, and concomitantly administered medications were recorded on the day rifampicin concentrations were measured. C(0) and C(2) were compared for differences regarding the presence or absence of side effects. Multivariate analysis was performed, with associated medications being taken into account. Seventy C(0) and 57 C(2) values were measured in 46 adults after a median treatment of 8 days (range, 1-179). Wide inter-individual variability was observed for C(0) and C(2). Thirteen (28%) patients reported GSE at least once. When GSE occurred, C(0) (median, 1 mg L(-1); range, 0.1-9.9 mg L(-1)) and C(2) (median, 10.3 mg L(-1); range, 1.8-40.3 mg L(-1)) were similar to C(0) (median, 0.6 mg L(-1); range, 0.1-10.3 mg L(-1)) and C(2) (median, 10.9 mg L(-1); range, 2.9-29.0 mg L(-1)) without GSE. The ALT value was more than normal in only three patients (6.5%) after rifampicin treatment began. The patients received no different associated medications whether or not GSE were present. Multivariate analysis showed no association between rifampicin plasma concentrations and GSE. GSE occur frequently in patients receiving rifampicin for osteoarticular infection but without an association with rifampicin plasma concentrations. Thus, therapeutic drug monitoring of rifampicin is irrelevant in the management of GSE.

Rifampicin (RFP) induces hepatic drug-metabolizing enzymes, making drug interactions a very important clinical problem. Clarithromycin (CAM) metabolism is reportedly enhanced by induction of hepatic drug-metabolizing enzymes (CYP3A4) by RFP, so that the blood lend of CAM decreases when RFP is administered concurrently. We connected an electrochemical detector to a high-performance liquid chromatograph (HPLC) for simple, rapid, easy measurement of blood concentrations of RFP and CAM. Using samples of patient serum, normal serum, and reference standards, we compared HPLC by an external laboratory and the results of LC/MS/MS analysis with those of this new assay. A strong correlation was seen between our HPLC results and those of the external laboratory in RFP levels (r=0.975, p<0.01). A strong correlation was also seen between results we obtained for CAM with the electrochemical detector in this assay and values measured by LC/MS/MS analysis (r=0.995, p<0.01). Our method enabled simple, rapid measurement of RFP and CAM by connecting the HPLC and electrochemical detector in tandem. This system was used to modulate dosage during combined therapy with RFP and CAM. The therapeutic effect for nontuberculous mycobacteriosis is expected to improve, and our HPLC is expected to be useful for simple, rapid, easy measurement of blood concentrations.

Rifampin is a key drug for tuberculosis (TB) treatment. The available data suggest that the currently applied 10-mg/kg of body weight dose of rifampin may be too low and that increasing the dose may shorten the treatment duration. A double-blind randomized phase II clinical trial was performed to investigate the effect of a higher dose of rifampin in terms of pharmacokinetics and tolerability. Fifty newly diagnosed adult Indonesian TB patients were randomized to receive a standard (450-mg, i.e., 10-mg/kg in Indonesian patients) or higher (600-mg) dose of rifampin in addition to other TB drugs. A full pharmacokinetic curve for rifampin, pyrazinamide, and ethambutol was recorded after 6 weeks of daily TB treatment. Tolerability was assessed during the 6-month treatment period. The geometric means of exposure to rifampin (area under the concentration-time curve from 0 to 24 h [AUC(0-24)]) were increased by 65% (P < 0.001) in the higher-dose group (79.7 mg.h/liter) compared to the standard-dose group (48.5 mg.h/liter). Maximum rifampin concentrations (C(max)) were 15.6 mg/liter versus 10.5 mg/liter (49% increase; P < 0.001). The percentage of patients for whom the rifampin C(max) was > or =8 mg/liter was 96% versus 79% (P = 0.094). The pharmacokinetics of pyrazinamide and ethambutol were similar in both groups. Mild (grade 1 or 2) hepatotoxicity was more common in the higher-dose group (46 versus 20%; P = 0.054), but no patient developed severe hepatotoxicity. Increasing the rifampin dose was associated with a more than dose-proportional increase in the mean AUC(0-24) and C(max) of rifampin without affecting the incidence of serious adverse effects. Follow-up studies are warranted to assess whether high-dose rifampin may enable shortening of TB treatment.

The bioavailability of rifampicin (RIF) in a fixed dose combination (FDC) used for the treatment of tuberculosis remains an area of clinical concern and several pharmaceutical alternatives are being explored to overcome this problem. The present study presents a pharmacological approach in which the bioavailability of a drug may be modulated by utilizing the herb-drug synergism. The pharmacokinetic interaction of some herbal products and a pure molecule isolated from Cuminum cyminum with RIF is shown in this paper. An aqueous extract derived from cumin seeds produced a significant enhancement of RIF levels in rat plasma. This activity was found to be due to a flavonoid glycoside, 3',5-dihydroxyflavone 7-O-beta-D-galacturonide 4'-O-beta-D-glucopyranoside (CC-I). CC-I enhanced the Cmax by 35% and AUC by 53% of RIF. The altered bioavailability profile of RIF could be attributed to a permeation enhancing effect of this glycoside., (Copyright (c) 2006 John Wiley & Sons, Ltd.)

The effect of colistin on bacterial eradication and survival was tested in experimental infection by multidrug-resistant Acinetobacter baumannii. The thigh infection model was applied in 86 neutropenic Wistar rats. Six rats were used for the induction of neutropenia and for the selection of the dose regimen of colistin; the remainder was equally divided into four groups: A, controls; B, rifampicin; C, colistin; and D, both agents. Therapy was administered 5 h after bacterial challenge; 5mg/kg of rifampicin was administered intravenously and 3mg/kg of colistin intramuscularly. Survival was recorded in 10 animals of each group. The remaining 10 rats per group were killed 4h after therapy; blood and tissue samples were sampled. Median survival of animals of groups A, B, C and D was 2.00, 2.50, 4.00 and 4.00 days, respectively (P=0.0048 between A and C and P=0.0012 between A and D. Mortality rates after 6 days of follow-up were 100, 100, 100 and 70%, respectively (P=0.018 between groups). Statistically significant decreases of bacteria were found in blood, liver, lung and spleen of group B compared with A; in lung of group C compared with A; and in blood and liver of group D compared with A. Colistin was effective in prolonging survival in an experimental thigh infection by multidrug-resistant A. baumannii in neutropenic rats. Its activity was enhanced after co-administration with rifampicin. These results mandate the application of colistin in the event of infections by multidrug-resistant pathogens and the need for its co-administration with rifampicin.

Monitoring of anti-tuberculosis drug concentrations and dose adjustment can be helpful in cases that show poor response to treatment. Here, we describe a method that can rapidly and simultaneously measure the blood concentrations of four anti-tuberculosis drugs (isoniazid, rifampicin, pyrazinamide, and ethambutol) and two major metabolic ratios (acetylisoniazid/isoniazid and 25-desacetylrifampicin/rifampicin) using high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). A C18 reversed-phase column and gradients of methanol in 0.3% formic acid and water were used for HPLC separation. The drug concentrations were determined by multiple reaction monitoring in positive ion mode and the assay performance was evaluated. We determined peak concentration ranges for each drug and acetylisoniazid/isoniazid and 25-desacetylrifampicin/rifampicin ratios by analyzing 2-h post-dose samples in patients treated with standard dosing as a first-line treatment. The preparation of 20 samples including two steps of deproteinization with 50% and 100% methanol was performed within 20 min and chromatographic separation was achieved within 4 min/sample. Interassay calibration variability data obtained over concentrations of 0-8 microg/mL for isoniazid and ethambutol and 0-80 microg/mL for rifampicin and pyrazinamide showed a linear and reproducible curve. Within-run and between-run imprecision (CVs) were 1.9-5.5% and 3.5-10.5% and the lower limits of detection and quantification were 0.01-0.5 microg/mL and 0.05-1.0 microg/mL, respectively. The isoniazid concentration was found to be inversely correlated to the acetylisoniazid/isoniazid ratio (R=-0.739, P<0.001). The devised method allows for the simple, rapid, sensitive and reproducible quantification of isoniazid, rifampicin, pyrazinamide, ethambutol and their two metabolic ratios and should be helpful for therapeutic drug monitoring in tuberculosis patients., (Copyright (c) 2007 John Wiley & Sons, Ltd.)

Antimicrobial efficacy in orthopedic device infections is diminished because of bacterial biofilms which express tolerance to antibiotics. Recently, the use of high doses of levofloxacin with rifampin has been recommended for staphylococcal infections. In the present study, we evaluated the efficacy of levofloxacin at doses of 50 mg/kg/day and 100 mg/kg/day (mimicking the usual and high human doses of 500 mg/day and 750 to 1,000 mg/day, respectively) and compared it to that of to linezolid, cloxacillin, vancomycin, and rifampin in a rat tissue cage model of experimental foreign-body infection by Staphylococcus aureus. The antimicrobial efficacy in vitro (by MIC, minimum bactericidal concentration, and kill curves) for logarithmic- and stationary-phase bacteria was compared with the in vivo efficacy. In vitro bactericidal activity at clinically relevant concentrations was reached by all drugs except rifampin and linezolid in the log-phase studies but only by levofloxacin in the stationary-phase studies. The bacterial count decreases from in vivo tissue cage fluids (means) for levofloxacin at 50 and 100 mg/kg/day, rifampin, cloxacillin, vancomycin, linezolid, and controls, respectively, were: -1.24, -2.26, -2.1, -1.56, -1.47, -1.15, and 0.33 (all groups versus controls, P < 0.05). Levofloxacin at 100 mg/kg/day (area under the concentration-time curve/MIC ratio, 234) was the most active therapy (P = 0.03 versus linezolid). Overall, in vivo efficacy was better predicted by stationary-phase studies, in which it reached a high correlation coefficient even if the rifampin group was excluded (r = 0.96; P < 0.05). Our results, including in vitro studies with nongrowing bacteria, pharmacodynamic parameters, and antimicrobial efficacy in experimental infection, provide good evidence to support the use of levofloxacin at high doses (750 to 1,000 mg/day), as recently recommended for treating patients with orthopedic prosthesis infections.

Few reports have addressed neonatal rifampicin plasma concentrations and data on neonatal rifampicin pharmacokinetics are completely lacking. Therefore, plasma concentrations of rifampicin and its main metabolite 25-O-desacetylrifampicin (DES) were measured in 123 surplus plasma samples from routine vancomycin monitoring in 21 neonates using reversed-phase HPLC. Rifampicin peak and trough plasma concentrations were 4.66 +/- 1.47 mg/L and 0.21 +/- 0.20 mg/L, respectively, after a dose of 8.5 +/- 2.1 (mean +/- SD) mg/kg per day. A significant linear relationship between rifampicin dose and peak plasma concentrations was found, but inter-patient variability was high. Pharmacokinetic parameters of rifampicin were calculated according to a one-compartment open model with iterative two-stage Bayesian fitting (MW\PHARM 3.60, Mediware, The Netherlands). First-order elimination constant, volume of distribution corrected for weight, total body clearance corrected for weight (CL/W), and elimination half-life were 0.16 +/- 0.06 h(-1), 1.84 +/- 0.59 L/kg, 0.28 +/- 0.11 Lkg(-1) h(-1), and 4.9 +/- 1.7 h, respectively. A high Pearson correlation was found between CL/W rifampicin and the covariates plasma creatinine and CL/W gentamicin of a preceding gentamicin treatment course, r = 0.728 (n = 17) and r = 0.837 (n = 12), respectively. DES was detected in each plasma sample. Therefore, rifampicin seems to be eliminated by both renal and metabolic pathways in neonates. In 8 study patients, plasma concentrations of rifampicin and DES were measured again after two weeks of therapy. CL/W rifampicin was significantly higher (67 +/- 50%). The authors suggest maintaining the current dose regimen of 10 mg/kg once a day. Because of the large inter-patient variability in rifampicin plasma concentrations and CL/W increase during therapy, the authors suggest monitoring rifampicin peak and trough plasma concentrations to avoid low plasma concentrations. More research is needed to determine well-founded dosing guidelines.

A simple and rapid high-performance liquid chromatographic (HPLC) method with ultraviolet detection has been developed and validated for the simultaneous determination of rifampicin and sulbactam in mouse plasma. Plasma samples were deproteinized with acetonitrile and separated by HPLC on a RP-18 (125 x 4 mm, 5 microm) column and gradient elution with potassium dihydrogen phosphate solution (pH 4.5; 50 mm) and acetonitrile at a flow-rate of 1.0 mL/min. Rifampicin and sulbactam were monitored at 230 nm and confirmed by means of their UV spectra using a diode-array detector. The method was linear at plasma levels from 1 to 100 microg/mL for rifampicin and from 5 to 200 microg/mL for sulbactam. The limits of quantification were 0.6 microg/mL for rifampicin and 4.2 microg/mL for sulbactam. The intra- and inter-day precisions of the method (RSD) were lower than 5% for both compounds. Average recoveries of rifampicin and sulbactam from mice plasma were 98.2 and 89.3%, respectively. The developed method was successfully applied to the determination of the pharmacokinetic profile of both compounds in mice., (Copyright 2005 John Wiley & Sons, Ltd.)

Two simple and accurate spectrophotometric methods for determination of Rifampicin (RIF) are described. The first method is based on charge transfer (CT) complex formation of the drug with three pi-electron acceptors either 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 7,7,7,8-Tetracyanoquinodimethane (TCNQ) or 2,3,5,6-Tetrachloro-1,4-benzoquinone (p-chloranil) in acetonitrile. The method is followed spectrophotometrically by measuring the maximum absorbance at 584 nm, 761 nm (680 nm) or 560 nm for DDQ, TCNQ and p-chloranil, respectively. Under the optimized experimental conditions, the calibration curves showed a linear relationship over the concentration ranges of 5-140 microg/ml, 2-45 microg/ml (5-120 microg/ml) and 15-200 microg/ml, respectively. The second method is based on the reaction of RIF with iron(III) forming a water insoluble violet complex which is extracted into chloroform. The method determines RIF in concentration range of 10-240 microg/ml at 540 nm. The proposed methods applied to determination of RIF in capsule, human serum and urine samples with good accuracy and precision. The results were compared statistically with the official method and showed no significant different between the methods compared in terms of accuracy and precision.

We studied the effect of rifampicin on steady-state pharmacokinetics of nevirapine and the impact of increasing the dose of nevirapine on its peak (Cmax) and trough (Cmin) levels in 13 HIV-infected patients on regular antiretroviral treatment with nevirapine-containing regimens (200 mg twice daily). A baseline pharmacokinetic study was conducted and repeated after 1 week of daily rifampicin (450/600 mg). The study was repeated in 7 of 8 patients who had subtherapeutic Cmin nevirapine levels after increasing nevirapine dose to 300 mg twice daily. Liver function was monitored. Rifampicin caused significant reductions in Cmax (42%), Cmin (53%), and exposure (46%) of nevirapine (P <.01). The Cmin of nevirapine fell below the therapeutic range of 3 microg/ml in 8 of 13 patients. An increase of nevirapine to 300 mg twice daily raised Cmin to therapeutic range in all 7 patients without exceeding the toxic level of 12 microg/mL. There were no clinical or laboratory adverse events. Our findings suggest that decreased bioavailability of nevirapine because of rifampicin coadministration could be overcome by increasing the dose of nevirapine from 200 to 300 mg twice daily without short-term adverse events. Further studies to evaluate the long-term safety of higher dose of nevirapine are required.

This study was designed to evaluate the pharmacokinetics and tissue distribution of free and alginate-encapsulated antitubercular drugs in mice at different doses. Alginate nanoparticles encapsulating isoniazid (INH), rifampicin (RIF), pyrazinamide (PZA) and ethambutol (EMB) were prepared by controlled cation-induced gelification of alginate. The formulation was orally administered to mice at two dose levels (D1 and D2). A comparison was made in mice receiving free drugs at equivalent doses. Drugs were analysed by high performance liquid chromatography (HPLC). The average size of alginate nanoparticles was found to be 235.5+/-0.0 nm with a polydispersity index of 0.44; drug encapsulation was 70-90% for INH and PZA, 80-90% for RIF and 88-95% for EMB. In the free drug groups, plasma levels of RIF and INH were higher and PZA and EMB levels were lower in the D1 group (per body surface area of mice) compared with the D2 group (recommended human dose). The plasma drug levels of all drugs were higher in the D1 encapsulated group compared with D2, resulting in higher values of area under the plasma drug concentration-time curve (AUC(0-infinity)). The relative bioavailabilities of all drugs encapsulated in alginate nanoparticles were significantly higher compared with free drugs. Drug levels were maintained at or above the minimum inhibitory concentration (MIC(90)) until Day 15 in organs after administration of encapsulated drugs, whilst free drugs stayed at or above the MIC(90) up to Day 1 only irrespective of dose. The levels of drugs in various organs remained above the MIC at both doses for equal periods, demonstrating their equiefficiency. Alginate nanoparticles hold great potential in reducing dosing frequency of antitubercular drugs.

Rifampicin, an antibacterial drug, is highly effective in the treatment of tuberculosis and leprosy. Recently, it has been reported to have neuroprotective effects in in vitro and in vivo models. This study was designed to elucidate its neuroprotective effects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity (known as an in vivo mouse model of Parkinson's disease). Mice were injected intraperitoneally (i.p.) with MPTP (10 mg/kg) four times at 1-h intervals, and brains were analyzed 3 or 7 days later. Rifampicin at 20 mg/kg (i.p., twice) had protective effects against MPTP-induced neuronal damage (immunohistochemical changes in tyrosine hydroxylase) in both the substantia nigra and striatum. Rifampicin also protected against the MPTP-induced depletions of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) in the striatum. The maximal concentrations of rifampicin between 30 and 240 min after a single rifampicin injection (20 mg/kg, i.p.) were 2.6 microM (at 30 min) in plasma and 0.77 microM (at 60 min) in striatum. Next, the effects of rifampicin on oxidative stress [lipid peroxidation in mouse brain homogenates and free radical-scavenging activity against diphenyl-p-picrylhydrazyl (DPPH)] were evaluated to clarify the underlying mechanism. At 1 microM or more, rifampicin significantly inhibited both lipid peroxidation in the striatum and free radical production. These findings suggest that in mice, rifampicin can reach brain tissues at concentrations sufficient to attenuate MPTP-induced neurodegeneration in the nigrostriatal dopaminergic neuronal pathway, and that an inhibitory effect against oxidative stress may be partly responsible for its observed neuroprotective effects.

Rifampicin has been found to be one of the most important antitubercular drugs; however, variable bioavailability of rifampicin in some fixed dose combinations (FDCs) as well as separate formulations has been reported in the literature. This resulted in proper evaluation of FDCs with standard protocol for bioequivalence trials. Earlier, plasma pooling as a rapid method for bioequivalence assessment of rifampicin in FDCs was proposed from our laboratory. Results obtained after pooled plasma sample analysis were compared with those from the individual plasma sample analysis. Case studies from our laboratories further validate and support the use of plasma pooling method as a faster and cost effective tool for bioequivalence assessment of rifampicin in FDCs, which will be useful in order to speed up the registration and approval of good quality FDCs., (Copyright 2006 Prous Science)

Aim: To study the effect of oral administration of crude aqueous extract of garlic for 14 days on pharmacokinetic parameters of isoniazid and rifampicin., Materials and Methods: Crude extract was prepared according to the method described by Fromtling and Bulmer. The study was done on 16 New Zealand white rabbits, divided into two groups of 8 animals each for two drugs. Baseline pharmacokinetic parameters for single-dose isoniazid and rifampicin were calculated from plasma drug concentrations obtained at various time intervals after dosing. The animals were given garlic extract orally for 14 days. Pharmacokinetic parameters were calculated again as done previously., Observations: Administration of crude aqueous extract of garlic significantly altered the pharmacokinetic parameters for isoniazid. C(max) was reduced from 15.4 +/- 5.6 to 5.4 +/- 3.3 microg/ml. AUC((0-24)) was reduced from 76.7 +/- 25.0 to 34.3 +/- 19.2 microg/ml.h. No significant change in T(max), k(el) and AUC((0-)(alpha)) was seen. Pharmacokinetic parameters of rifampicin were not significantly altered by administration of garlic extract., Conclusions: Oral administration of garlic extract decreased the bioavailability of isoniazid significantly with no change in rate of elimination. Bioavailability of rifampicin is not significantly altered by garlic extract., (Copyright 2006 S. Karger AG, Basel.)

Background: The pharmacokinetics of rifampin and ethambutol in HIV-infected patients with tuberculosis (TB) are incompletely characterized. We examined the pharmacokinetics of rifampin and ethambutol in a cohort of patients with HIV-related TB who were treated in the United States., Methods: Serum drug concentrations were determined 2, 6, and 10 h after dosing in 36 HIV-infected patients with TB who were taking rifampin and in 49 who were taking ethambutol. Observed serum concentrations were compared with published normal ranges and published data., Results: With daily dosing of rifampin (600 mg), 26 (77%) of 34 patients (95% confidence interval [CI], 59%-89%]) had a low maximum concentration of rifampin (<8 microg/mL), and 12 (35%; 95% CI, 20%-54%) had a very low maximum concentration (<4 microg/mL). With intermittent rifampin dosing (600 mg), 13 (68%) of 19 patients (95% CI, 44%-85%) had a low maximum concentration of rifampin, and 5 (26%; 95% CI, 11%-50%) had a very low maximum concentration. With daily ethambutol dosing (20 mg/kg), 33 (69%) of 48 patients (95% CI, 55%-81%) had a low maximum concentration of ethambutol (<2 microg/mL), and 18 (38%; 95% CI, 24%-53%) had a very low maximum concentration (<1 microg/mL). With intermittent ethambutol dosing (50 mg/kg twice weekly or 30 mg/kg thrice weekly), 13 (72%) of 18 patients (95% CI, 47%-88%) had a low maximum concentration of ethambutol (<4 microg/mL), and 5 (28%; 95% CI, 12%-54%]) had a very low maximum concentration (<2 microg/mL)., Conclusions: In HIV-infected patients with TB who are receiving rifampin and ethambutol, low maximum concentrations of rifampin and ethambutol were common. For patients with HIV-related TB, therapeutic monitoring of rifampin and ethambutol levels may help clinicians achieve target serum concentrations.

The present study was planned to evaluate the chemotherapeutic potential of nebulized solid lipid particles (SLPs) incorporating rifampicin, isoniazid and pyrazinamide against experimental tuberculosis. The SLPs prepared by the "emulsion solvent diffusion" technique possessed a favourable mass median aerodynamic diameter suitable for bronchoalveolar drug delivery. Following a single nebulization to guinea pigs, therapeutic drug concentrations were maintained in the plasma for 5 days and in the organs (lungs, liver and spleen) for 7 days whereas free drugs were cleared by 1-2 days. The mean residence time and drug bioavailability were improved several-fold in the case of drug-loaded SLPs. A similar pharmacokinetic profile was observed in Mycobacterium tuberculosis-infected guinea pigs. On nebulization of drug-loaded SLPs to infected guinea pigs at every 7th day, no tubercle bacilli could be detected in the lungs/spleen after 7 doses of treatment whereas 46 daily doses of orally administered drugs were required to obtain an equivalent therapeutic benefit. Further, there was no evidence of any biochemical hepatotoxicity. Thus, nebulization of SLP-based antitubercular drugs forms a sound basis for improving drug bioavailability and reducing the dosing frequency for better management of pulmonary tuberculosis.

To improve the rapidity of the registration process of rifampicin (RMP) containing fixed-dose combination (FDC) formulations, a plasma pooling methodology was used to increase the throughput of bioanalysis of plasma samples from bioequivalence trials of FDCs. Plasma samples of a biostudy were analysed for RMP using traditional analysis methods as well as a plasma pooling method (volunteer and time pooling). Both methods produced similar results, with less than 15% variability in both volunteer and time pooling. The plasma pooling method for bioanalysis was validated. Further studies are required to identify and reduce the percentage variability.

Leprosy, a chronic granulomatous infectocontagious disease transmitted by Mycobacterium leprae, continues to be prevalent today, especially in underdeveloped countries and its paucibacillary form with a single lesion is being treated with rifampicin (600mg), ofloxacin (400mg) and minocycline (100mg) administered as a single dose (ROM scheme). Thus, the objective of the present study was to investigate the dose/plasma concentration correlation versus biochemical changes occurring in male Wistar rats receiving a single dose of rifampicin, ofloxacin and minocycline in mono- and polytherapy. Rifampicin and ofloxacin showed an increased concentration in plasma when administered in polytherapy, whereas minocycline was reduced, probably due to interference with its biotransformation and excretion. Biochemical analyses showed that rifampicin is probably responsible for hepatic and renal changes and that the medicamentous interactions involving the drug require individualized studies, especially when the drug is associated with ofloxacin and minocycline therapy.

Rifampicin shows variable bioavailability from solid oral dosage forms and the reasons for this variable absorption reported in literature varies from extrinsic formulations factors to intrinsic variability in rifampicin absorption. Hence, we have undertaken a systematic and comprehensive evaluation of all the factors to study contribution of all the factors on rifampicin absorption. As a first step, data from eight bioequivalence studies conducted at National Institute of Pharmaceutical Education and Research (NIPER) bioavailability center was compared across the trials to understand the effect of extrinsic/intrinsic factors on the bioavailability of rifampicin, isoniazid and pyrazinamide. Out of eight fixed dose combination (FDC) formulations, six formulations were bioequivalent for rifampicin to separate formulations whereas one formulation was below and one was above the limits of bioequivalence. It was observed that more variability in rifampicin blood levels is associated with FDC formulations when compared to rifampicin-only formulations and was attributed to complexity involved in the manufacturing of FDCs. Further, one of the rifampicin-only capsule showed unexpectedly lower plasma levels indicating role of physical characteristics of rifampicin bulk material. It was also seen that rifampicin shows dose-dependent pharmacokinetics even at the modest increase in dose due to saturation of efflux system at absorption site and metabolizing enzymes for elimination. Other components of FDC formulations such as isoniazid and pyrazinamide due to high solubility and permeability have shown very less variability and were bioequivalent to separate formulations even from formulations those were failed for rifampicin. The comparison of data across the trials suggested that rifampicin bioavailability problem is more attributable to the extrinsic factors such as formulation or rifampicin bulk material rather than intrinsic variability of rifampicin absorption.

Cerebrospinal fluid (CSF) concentration-time curves of rifampicin and fusidic acid were studied in a patient with post-operative meningitis caused by Staphylococcus epidermidis. The patient was treated with this combination of antimicrobial agents because of a severe hypersensitivity reaction to vancomycin. Peak CSF concentrations of rifampicin exceeded the MIC by > 60-fold, while those of fusidic acid just reached the MIC. CSF concentrations of fusidic acid were relatively stable within the range reported for patients with uninflamed meninges, but serum levels were surprisingly low. An increase in the metabolism of fusidic acid induced by rifampicin cannot be excluded.

The effect of pefloxacin on the pharmacokinetics parameters of rifampicin in humans was investigated using plasma and saliva concentrations. Five healthy volunteers (4 male and 1 female), ages 20-35 years, each received 600 mg rifampicin alone, and after a 1-week drug washout period, 600 mg rifampicin plus 500 mg pefloxacin was administered with 350 mL of water. Plasma and saliva concentrations of rifampicin were measured at 7 different time intervals and different pharmacokinetics parameters calculated. Pefloxacin coadministered with rifampicin reduced plasma and saliva elimination half-life, peak plasma concentration, area under the concentration time curve, volume of distribution, minimum absorption time, absorption rate constant, and absorption half-life showed a significant increase (P < 0.05). Time to reach peak plasma concentration was not affected with or without pefloxacin. Pefloxacin increases bioavailability of rifampicin and hence extends its detection in the body as demonstrated by rifampicin being estimated at 24 hours when coadministered with pefloxacin, whereas at 24 hours, it was completely absent when administered alone.

Fixed dose combination (FDC) formulations became popular in the treatment of tuberculosis (TB) because of the better patient compliance, reduced risk of monotherapy and emergence of drug resistance in contrast to treatment with separate formulations of two to four first-line drugs. However, its successful implementation in national programs is limited by probable bioinequivalency of rifampicin if present in FDC form. In this regard, World Health Organization (WHO) and International Union Against Tuberculosis and Lung Disease (IUATLD) recommend FDCs only of proven bioavailability. Hence, bioequivalence study of four drug FDC tablet was conducted using 22 healthy male volunteers according to WHO recommended protocol to determine bioavailability of rifampicin, isoniazid and pyrazinamide compared to standard separate combination at the same dose level. The study was designed as two period, two treatment crossover experiment with a washout period of 1 week. Bioequivalence of rifampicin was estimated by plasma and urinary method for both rifampicin and its active metabolite, des-acetyl rifampicin whereas isoniazid and pyrazinamide were estimated from plasma. Mean concentration time profiles and all the pharmacokinetic parameters of rifampicin, isoniazid and pyrazinamide from FDC tablet were comparable to individual formulations and passed the bioequivalence test with power of the test above 95%. Further, bioequivalence of both rifampicin and isoniazid shows that in vitro interaction of rifampicin and isoniazid is clinically insignificant. Thus, it was concluded that FDC formulation is bioequivalent for rifampicin, isoniazid and pyrazinamide and ensures the successful treatment of TB without compromising therapeutic efficacy of any of these components of anti-TB therapy.

A HPLC-UV method has been developed for assaying rifampicin in plasma and liver. The assay involved a liquid-liquid extraction procedure with dichloromethane-pentane (1:1). An Ultrabase-C18 column and a simple mobile phase consisting of a water (pH 2.27)-acetonitrile (40:60, v/v) mixture were used. The flow-rate was 1 ml/min and the effluent was monitored at 333 nm. Results from the HPLC analyses showed that the assay method is linear in the ranges 0.1-1 and 1-50 microg/ml for plasma, and 0.6-40 microg/g for liver. Intra- and inter-day R.S.D. were below 15% for all the sample types. Recoveries averaged 83 and 95% for plasma and liver, respectively. The method is being successfully applied to determine rifampicin in plasma and liver samples taken during pharmacokinetic studies in rats.

Background and Objective: Rifampin (INN, rifampicin) causes several drug interactions with coadministered antidiabetic drugs. Rosiglitazone is a novel thiazolidinedione antidiabetic drug, but little is known about the drug interaction between rifampin and rosiglitazone. Our objective was to investigate the effect of rifampin on the pharmacokinetics of rosiglitazone in humans., Method: In an open-label, randomized, 2-way crossover study, 10 healthy Korean male subjects were treated once daily for 6 days with 600 mg rifampin or with placebo. On day 7, a single dose of 8 mg rosiglitazone was administered orally. Plasma rosiglitazone concentrations were measured., Results: Rifampin significantly decreased the mean area under the plasma concentration-time curve for rosiglitazone by 65% (2947.9 ng. h/mL versus 991.5 ng. h/mL, P <.001) and the mean elimination half-life from 3.9 to 1.5 hours (P <.001). The peak plasma concentration of rosiglitazone was significantly decreased by rifampin (537.7 ng/mL versus 362.3 ng/mL, P <.01). The apparent oral clearance of rosiglitazone increased about 3-fold after rifampin treatment (2.8 L/h versus 8.5 L/h, P <.001)., Conclusion: This study showed that rifampin affected the disposition of rosiglitazone in humans, probably by the induction of cytochrome P450 (CYP) 2C8 and, to a lesser extent, CYP2C9. Therefore caution should be exercised during the coadministration of rifampin and rosiglitazone.

Objective: To compare the steady-state plasma and intrapulmonary concentrations of oral rifampicin (rifampin) in men and women with and without AIDS., Design: Prospective nonblinded pharmacokinetic study., Participants: Ten men with AIDS, ten men without AIDS, ten women with AIDS, and ten women without AIDS., Methods: Rifampicin 600 mg was administered orally once daily for 5 days to 40 adult volunteers. Blood was obtained 2 hours after the last dose and at the time of bronchoalveolar lavage (BAL) performed 4 hours after the last dose. Rifampicin was measured in plasma, epithelial lining fluid (ELF) and alveolar cells. Standardised BAL was performed without systemic sedation. The volume of ELF was calculated by the urea dilution method, and alveolar cells were recovered by a standardised centrifugation technique. The volume of alveolar cells was calculated from the cell count and differential performed on the BAL fluid. Rifampicin was measured by high-performance liquid chromatography., Results: Sex or AIDS status had no effect on plasma concentrations of rifampicin at 2 hours, 4 hours, or in ELF. Plasma concentrations (mean +/- SD) of rifampicin at 2 hours (9.15 +/- 5.4 mg/L) were not significantly different (p > 0.05) from those at 4 hours (9.10 +/- 5.6 mg/L) following the last dose. The ELF concentration was 2.0 +/- 1.6 mg/L with a range of 0-7.3 mg/L and the ELF/plasma ratio at 4 hours was 0.2 +/- 0.2. Rifampicin was not detectable in ELF in eight subjects (three with AIDS and five without AIDS) or in alveolar cells in three subjects without AIDS. There was no significant effect of AIDS on alveolar cell concentrations of rifampicin. Alveolar cell concentrations of rifampicin were significantly greater in women (13.9 +/- 6.7 mg/L) than in men (6.6 +/- 4.1 mg/L) [p = 0.0003]. Alveolar cell rifampicin concentrations were 78% greater in smoking women (17.8 +/- 7.0 mg/L) than in nonsmoking women (10.0 +/- 2.4 mg/L), but the difference was not significant (p > 0.05). CD4+ cell counts in the AIDS subjects were not correlated with the concentrations of rifampicin in plasma, ELF or alveolar cells., Conclusions: The absorption of oral rifampicin was not affected by sex or AIDS. Plasma and alveolar cell concentrations were not significantly different, were both greater than ELF concentrations, and were adequate to inhibit Mycobacterium tuberculosis. Considerable interpatient variability was detected despite witnessed drug administration. The clinical significance of these findings is unknown but merits further investigation.

Rifampicin is one of the most important first line drugs used in fixed dose combinations (FDCs) of antitubercular drugs. The chances of reduced bioavailability of rifampicin from FDCs necessitated its evaluation against standard formulations of individual drugs in bioequivalence studies. This study was undertaken to evaluate the importance of plasma pooling methodology as a rapid and cheaper tool to evaluate bioequivalence of rifampicin component of FDCs of antitubercular drugs. Plasma samples of volunteers obtained from bioequivalence studies were pooled according to volunteer and time-wise pooling. Area under the plasma concentration versus time curves (AUCs) of rifampicin was reduced in the pooled plasma samples when compared to the individual samples. However, the ratio of AUCs of FDCs to that of separate formulations was found to be comparable for both the individual samples and pooled samples data. Concentration-time profiles of rifampicin obtained after time-wise pooling were subjected to non-compartmental analysis for determination of pharmacokinetic parameters. Whereas bioequivalence estimates were determined using individual AUC values obtained from volunteer-wise pooling. Results indicated the possibility of using plasma pooling methodology in bioequivalence estimation of rifampicin to simplify and accelerate the registration process.

Objective: This study was performed to elucidate the pharmacokinetic profiles of antimycobacterial regimens for peritoneal dialysis patients., Patients: Nine patients on maintenance continuous ambulatory peritoneal dialysis (CAPD) were included in this study., Methods: After administering a conventional oral dose of antituberculosis medications, we measured plasma and peritoneal fluid concentrations of isoniazid by fluorometry, and rifampin and pyrazinamide by high performance liquid chromatography. The assay data were subjected to pharmacokinetic analysis., Results: Average peak plasma concentrations of isoniazid, rifampin, and pyrazinamide were 3.3 mg/L, 6.5 mg/L, and 30.9 mg/L, respectively, all of which much exceed the minimum inhibitory concentration (MIC) for Mycobacterium tuberculosis. Peritoneal fluid concentrations of isoniazid and pyrazinamide were maintained well above the MICs for M. tuberculosis; however, peritoneal fluid concentration of rifampin was below the therapeutic range most of the time., Conclusion: For the treatment of systemic or pulmonary tuberculosis in CAPD patients, no dose adjustments are required for isoniazid, rifampin, or pyrazinamide. On the contrary, for the treatment of tuberculous peritonitis, oral rifampin therapy is not expected to be effective because of its low peritoneal fluid concentration.

Background: Current therapeutic regimens with rifampicin and isoniazid have proven successful in treating tuberculosis, however, toxicity, therapeutic failure, relapse and multiple drug resistance are serious concerns. Optimizing drug dose using therapeutic drug monitoring (TDM) may be a better approach than administering therapy as a standard dose., Aims: To establish and evaluate a TDM service to optimize rifampicin and isoniazid therapy., Methods: A TDM service for rifampicin and isoniazid was established in November 1998. Drug concentration data were collected, with relevant information to interpret the results. The reason for the request, information on concomitant drug administration and a questionnaire to assess clinical response to the drug results were also obtained., Results: Ninety patient episodes were accepted for study. The rifampicin plasma concentrations showed significant scatter, with 46% of the rifampicin concentrations below the normal range and 2% above the normal range. Similarly, 48% of isoniazid concentrations were below the lower target of the normal range and 29% were above the upper normal limit. There was a greater proportion of isoniazid concentrations above the normal range in female patients., Conclusion: Significant pharmacokinetic variability was observed for rifampicin and isoniazid in the patient population studied. Further, a substantial number of plasma concentrations fell outside the suggested normal range for both drugs. Isoniazid plasma concentrations were significantly higher in female patients compared with male patients. Despite these abnormal results, the dose of rifampicin and isoniazid was altered in only 17% of patients, however, many patients received follow-up education because of the drug result. The service was considered valuable by 83% of respondents to the questionnaire. While TDM of rifampicin and isoniazid is a valuable tool to optimize the dose of these drugs in some patients, there is an urgent need for concentration-effect studies and possibly education on the principles and practice of TDM for these drugs.

The time course of rifampicin and miconazole concentrations after insertion of a polyurethane catheter loaded with these antibiotics were studied. Data from controlled release experiments in vitro were used, and the concentration time courses of the antimicrobials in serum were calculated by pharmacokinetic simulations. Systemic therapy using typical dosages (rifampicin 600 mg/day iv, miconazole 3 x 200 mg/day iv) results in rifampicin concentrations between 54 and 8424 microg/L, and miconazole concentrations between 3567 and 4676 microg/L. After insertion of a polyurethane catheter loaded with these antibiotics, the maximal concentrations after catheter placement were determined as 6 microg/L at 10.7h for rifampicin, and 13 microg/L at 28.6 h for miconazole. Assuming that the total amount of antibiotics incorporated in the catheter matrix were bioavailable ('worst case'), the resulting maximal concentrations calculated by simulation are 10 microg/L for rifampicin and 65 microg/L for miconazole. Maximal concentrations of rifampicin or miconazole resulting from the insertion of a polyurethane catheter loaded with these antibiotics are, therefore, far below the concentrations resulting from a systemic therapy with the same antimicrobial agents. Even in the worst case, the danger of selecting resistant bacterial strains seems remote because the systemic drug levels are magnitudes of order below subinhibitory concentrations., (Copyright 2003 The Hospital Infection Society)

The concentrations of rifampicin in epithelial lining fluid (ELF), human alveolar macrophages (AM), bronchial mucosal biopsies and serum were measured after a single oral dose of 600 mg rifampicin from 15 patients undergoing fibre-optic bronchoscopy. The samples of ELF, AM, the bronchial mucosal biopsies and serum were obtained approximately 2-5 h after dosing. The mean concentrations (mean +/- standard error) were 5.25 mg/L (+/-0.67) in ELF, 7.93 mg/kg (+/-1.61) in bronchial biopsies, 15.48 mg/L (+/-1.41) in serum and 251.8 mg/L (+/-65.92) in alveolar macrophages. These site concentrations exceeded the MIC90 for common respiratory pathogens including Mycobacterium tuberculosis and support the observed clinical efficacy of rifampicin in the treatment of a wide range of respiratory tract infections.

Complex drug interactions involving antiretroviral agents and drugs for the management of opportunistic infections demand the monitoring of plasma drug concentrations to prevent treatment failure. The high occurrence of tuberculosis in HIV-infected subjects makes the management of HIV treatment complex. Rifampicin, a potent inducer of the cytochrome P 450 metabolic pathway, is a very active antituberculosis drug that accelerates the metabolism of protease inhibitors. Regimens containing efavirenz, a non-nucleoside reverse transcription inhibitor, could be an alternative, but efavirenz plasma concentrations may be altered after the coadministration of rifampicin. Efavirenz is also a cytochrome P 450 inducer and may alter rifampicin plasma levels. Due to the increasing need to monitor plasma concentrations in HIV patients with tuberculosis, a high-performance liquid chromatographic (HPLC) method has been developed to measure rifampicin and efavirenz at the same time in a small amount of sample. This HPLC method is highly sensitive and precise, suitable for pharmacokinetic studies or routine clinical monitoring of rifampicin and efavirenz simultaneously in HIV patients with tuberculosis.

Depending on the patient category, tuberculosis requires treatment with 3 to 5 drugs which means that patient's compliance to therapy may not be optimal. To increase patient's adherence to treatment schedules, these drugs can be given as single drug preparations or fixed dose combinations (FDCs) of 2 or more drugs in a single formulation. However, an important issue associated with a rifampicin-containing FDC is its quality. Hence, to avoid spurious formulations entering the market, the World Health Organization and the International Union Against Tuberculosis and Lung Disease have recommended FDCs only of proven bioavailability. In this study, the relative bioavailability of rifampicin, isoniazid and pyrazinamide was assessed in a group of 14 healthy male subjects using the FDC tablet containing 4 drugs versus separate formulations at the same dose levels. The study was designed as an open, crossover trial. A total of 9 blood samples were collected over a period of 24 h. The concentration of rifampicin, its main metabolite desacetyl rifampicin, isoniazid and pyrazinamide in plasma were assessed using HPLC analysis. The pharmacokinetic parameters AUC(0-24) and Cmax were subjected to parametric and non-parametric statistical tests at 90% confidence interval. In addition, time to reach peak concentration (tmax), elimination rate constant (Kel) and terminal elimination half-life (t1/2) for each drug were also calculated. It was concluded that the FDC tablet containing 4 drugs is bioequivalent to separate rifampicin, isoniazid and pyrazinamide formulations at the same dose levels.

Tuberculosis (TB) needs treatment with three to five different drugs simultaneously, depending on the patient category. These drugs can be given as single drug preparations or fixed dose combinations (FDCs) of two more drugs in a single formulation. World Health Organization and International Union against Tuberculosis and Lung Disease (IUATLD) recommend FDCs only of proven bioavailability. The relative bioavailability of rifampicin (RIF), isoniazid (INH) and pyrazinamide (PYZ) was assessed on a group of 13 healthy male subjects from a four drug FDC versus separate formulations at the same dose levels. The study was designed to be an open, crossover experiment. A total of nine blood samples each of 3 ml volume were collected over a period of 24-h. The concentrations of RIF, its main metabolite desacetyl RIF (DRIF), INH and PYZ in plasma were assessed by HPLC analysis. Pharmacokinetic parameters namely AUC(0-24), AUC(0-inf), C(max), T(max), were calculated and subjected to different statistical tests (Hauschke analysis, two way ANOVA, normal and log transformed confidence interval) at 90% confidence interval. In addition, elimination rate constant (K(el)) and absorption efficiencies for each drug were also calculated. It was concluded that four drugs FDC tablet is bioequivalent for RIF, INH and PYZ to separate formulation at the same dose levels.

Isoniazid (IN), pyrazinamide (Pz) and rifampicin (Rf) are separated on YMC-ODS column. IN was derivatized with 2-fluorene-carboxaldehyde (FA). The separation was achieved using ethanol-chloroform-acetonitrile water by isocratic elution and detected at 337 nm. The detection limits were 0.11 ng, 0.2 ng and 13 ng/injection (5 microl) for IN, Pz and Rf, respectively. The method of analysis was applied to the pharmaceutical preparations and in the blood samples of the patients suffering from tuberculosis after undergoing chemotherapy with IN, Pz and Rf. The amounts quantitated in blood showed 0.97 to 1.58 microg/ml IN, 3.44 to 4.09 microg/ml Pz and 1.98 to 3.5 microg/ml Rf with coefficient of variations 0.8-1.8%, 0.9-1.3% and 0.8-2.1%, respectively.

Bioanalytical methods using automated 96-well solid-phase extraction (SPE) and liquid chromatography with electrospray tandem mass spectrometry (LC/MS/MS) are widely used in the pharmaceutical industry. SPE methods typically require manual steps of drying of the eluates and reconstituting of the analytes with a suitable injection solvent possessing elution strength weaker than the mobile phase. In this study, we demonstrated a novel approach of eliminating these two steps in 96-well SPE by using normal-phase LC/MS/MS methods with low aqueous/high organic mobile phases, which consisted of 70-95% organic solvent, 5-30% water, and small amount of volatile acid or buffer. While the commonly used SPE elution solvents (i.e. acetonitrile and methanol) have stronger elution strength than a mobile phase on reversed-phase chromatography, they are weaker elution solvents than a mobile phase for normal-phase LC/MS/MS and therefore can be injected directly. Analytical methods for a range of polar pharmaceutical compounds, namely, omeprazole, metoprolol, fexofenadine, pseudoephedrine as well as rifampin and its metabolite 25-desacetyl-rifampin, in biological fluids, were developed and optimized based on the foregoing principles. As a result of the time saving, a batch of 96 samples could be processed in one hour. These bioanalytical LC/MS/MS methods were validated according to "Guidance for Industry - Bioanalytical Method Validation" recommended by the Food and Drug Administration (FDA) of the United States.

Objective: To evaluate the pharmacokinetic interactions between efavirenz and rifampicin (rifampin) in patients with HIV infection and tuberculosis., Design: Nonblind, randomised, pharmacokinetic study., Patients: 24 patients (21 male, 3 female; mean age 37 years) with HIV infection and tuberculosis., Interventions: Patients were randomised to one of the following treatments: group A (n = 16) received antituberculosis drugs without rifampicin, plus highly active antiretroviral therapy (HAART) including efavirenz 600 mg once daily, on days 1 to 7. Patients were then switched to rifampicin in bodyweight-adjusted fixed-dose combination plus HAART including efavirenz 600 mg once daily (group A-1; n = 8) or efavirenz 800 mg once daily (group A-2; n = 8). Group B (n = 8) received rifampicin in bodyweight-adjusted fixed-dose combination on days 1 to 7; on day 8, HAART including efavirenz 800 mg once daily was added. Blood samples were obtained on days 7 and 14., Methods: Plasma concentrations of efavirenz and rifampicin were quantified by using validated high performance liquid chromatography assays, and pharmacokinetic parameter values were determined by noncompartmental methods. The differences between pharmacokinetic parameters on days 7 and 14 were used to assess interactions., Results: There was a correlation between the pharmacokinetic parameters of efavirenz and the dose/kg administered. For efavirenz, mean (median) peak concentration, trough concentration and area under the concentration-time curve over the administration interval decreased 24% (24%), 25% (18%) and 22% (10%), respectively, in the presence of rifampicin. Large interpatient variability was observed, suggesting that plasma concentration monitoring of efavirenz may be advisable. Overall, the pharmacokinetics of efavirenz 800 mg plus rifampicin were similar to those of efavirenz 600 mg without rifampicin. The pharmacokinetics of rifampicin did not change substantially in the presence of efavirenz. Differences in patients' bodyweight appeared to cause further differences in exposure to efavirenz. Plasma concentrations of efavirenz in patients weighing <50 kg were similar to those previously described in HIV-infected patients without concomitant tuberculosis. However, plasma concentrations in patients weighing >or=50 kg were almost halved compared with those in patients weighing <50 kg., Conclusions: Although the minimal effective efavirenz plasma concentration that assures virological success is not currently known, it may be advisable to increase the dosage of efavirenz to 800 mg once daily when it is coadministered with rifampicin. Rifampicin can be used with efavirenz without dosage modification.