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Leprosy continues to be the belligerent public health hazard for the causation of high disability and eventual morbidity cases with stable prevalence rates, even with treatment by the on-going multidrug therapy (MDT). Today, dapsone (DDS) resistance has led to fear of leprosy in more unfortunate people of certain developing countries. Herein, DDS was chemically conjugated with five phytochemicals independently as dapsone-phytochemical conjugates (DPCs) based on azo-coupling reaction. Possible biological activities were verified with computational chemistry and quantum mechanics by molecular dynamics simulation program before chemical synthesis and spectral characterizations viz., proton-HNMR, FTIR, UV and LC-MS. The in vivo antileprosy activity was monitored using the 'mouse-foot-pad propagation method', with WHO recommended concentration 0.01% mg/kg each DPC for 12 weeks, and the host-toxicity testing of the active DPC4 was seen in cultured-human-lymphocytes in vitro. One-log bacilli cells in DDS-resistant infected mice footpads decreased by the DPC4, and no bacilli were found in the DDS-sensitive mice hind pads. Additionally, the in vitro host toxicity study also confirmed that the DCP4 up to 5,000 mg/L level was safety for oral administration, since a minor number of dead cells were found in red color under a fluorescent microscope. Several advanced bioinformatics tools could help locate the potential chemical entity, thereby reducing the time and resources required for in vitro and in vitro tests. DPC4 could be used in place of DDS in MDT, evidenced from in vivo antileprosy activity and in vitro host toxicity study.

Intracellular localization of antileprosy drugs dapsone (DDS) and rifampicin (RFP) was carried out on skin and nerve lesions obtained from multidrug treated, multi (BL-LL)- and pauci (BT-TT) bacillary cases of leprosy using immunocytochemical techniques. Intracellular localization of the above drugs especially in macrophages and Schwann cells was aimed by using rabbit raised anti DDS and RFP polyclonal antibody in an indirect peroxidase assay. Our study records both intra and extracellular staining with anti DDS and RFP antibodies in the skin as well as nerve lesions of MB and PB cases treated with MDT. All the nerves under investigation had moderate to severe pathology and hence free diffusion of the drug could be attributed to the broken barrier. Basal lamina around the Schwann cell did not seem to form a barrier. It was also noted that the drug (metabolite) persisted over a long period of time).

The half time of disappearance of dapsone and monoacetyl dapsone and the acetylator phenotype of the leprosy patients who harboured dapsone sensitive and dapsone resistant M. leprae was assessed in 27 subjects. Sixteen patients were rapid acetylators, five were slow and six were intermediate acetylators. The mean T 1 1/2 lives of dapsone (30.26 +/- 11.0) and monoacetyl dapsone (31.11 +/- 12.0) were also studied in the above patients. The percentage of different acetylators in both resistant and sensitive groups were similar showing no correlation between the emergence of drug resistance and the phenotype of the patient. The mean time of disappearance of DDS and MAD in the different acetylators did not show significant difference. The ratios of MAD/DDS in an individual at 3, 6 or 24 hours after the dose were similar. The mean T 1 1/2 lives of DDS and MAD in resistant and sensitive patients also showed no difference. Neither T 1 1/2 lives of DDS or MAD nor the acetylator phenotype seem to influence the emergence of dapsone resistance.

Fifteen untreated leprosy patients were given rifampicin and dapsone for seven days, and then rifampicin, dapsone and clofazimine for seven days. Concentrations of rifampicin and dapsone were estimated in timed plasma specimens and in 24 h urine specimens on days 7 and 14. No significant differences in the pharmacokinetics of rifampicin and dapsone were observed between the two occasions of sampling.

Dapsone (DDS) in urine of 250 leprosy patients collected on surprise visits were screened by simple paper spot, tile tests and sensitive Enzyme linked immunosorbent assay (ELISA) and Haemagglutination inhibition (HI) tests. The urinary DDS concentration as well as DDS/C ratios were also studied. Simultaneously, 50 microliter of blood was collected from each of these patients and its dapsone content was estimated by HPLC. Urine samples with means of 25 to 30 micrograms/ml DDS and 55-64 micrograms/mg DDS/C ratios were found to give positive tests by any of the above screening procedures, while their mean blood DDS concentration was found to be 0.91 microgram/ml. The corresponding values for those specimens giving negative tests were 3.8 to 5.7 micrograms DDS per ml and 9 to 13 micrograms/mg DDS/C ratio. The blood DDS concentration in this group was ranging from 0.16 to 0.18 micrograms/ml. The findings are discussed in relation to their metabolic significance and their application in a leprosy control programme.

Pharmacokinetics of aspirin and chloramphenicol was studied in 16 normal and 16 patients suffering from leprosy. A significant increase (p less than 0.05) in the elimination half-life of chloramphenicol was observed before and after dapsone treatment in leprotic patients as compared with the normal volunteers, while no significant difference was observed in any of the pharmacokinetic parameters with aspirin.

In order to determine the suitability of the armadillos as a model of human leprosy for chemotherapeutic studies, especially in evaluating newer anti-leprosy drugs, uninfected Armadillos were used to study the metabolic disposition of DDS. Serum DDS levels ranged from 500 ng/ml at 3 hours to 13 ng/ml at 96 hours after intravenous administration of DDS (1 mg/kg). In an ad libitum feeding trial of DDS it was found that the level of serum DDS varied according to the dose of DDS, and even at a dose of 0.0001%, the animals maintained MIC of DDS against M. leprae. Finally, it was demonstrated that armadillos acetylate DDS to MADDS and 7-9% of DDS is acetylated by armadillos.

In 22 lepromatous Filipino patients receiving their first injection of 225 mg acedapsone (DADDS), dapsone (DDS), and monoacetyl DDS (MADDS) were present in plasma in approximately equal quantities. Peak levels of parent drug, DDS, and MADDS occurred between 22 and 35 days. The half-times of disappearance (T1/2) from plasma were 43 days for DDS and MADDS and 46 days for DADDS. Acetylator phenotyping with sulfamethazine (SMZ) and DDS showed that 17 patients were rapid and 5 patients were slow acetylators. Correlations between acetylation of SMZ and DDS after DDS and of acetylation of DDS after DDS and DADDS were highly significant. However, acetylation of DDS after DADDS did not differentiate the patients into acetylator phenotypes. The T1/2 of DDS after DDS in the patients was directly related to the minimum levels of DDS at 77 days after DADDS treatment. These minimum levels were 8-fold higher than the minimum inhibitory concentration (MIC) of DDS for Mycobacterium leprae in mice and rats, but not all patients responded satisfactorily. No relationship could be demonstrated between the bacteriologic response and any of the pharmacologic parameters examined in these Filipino patients. In a companion study, minimum levels of DADDS, MADDS, and DDS were determined in 447 leprosy patients of all disease types from the Karimui District of Papua New Guinea who had been receiving 225 mg DADDS every 70 to 80 days for the past 5 years. All patients exhibited DDS levels above the MIC of DDS for M. leprae, no significant differences in plasma sulfone levels were found among disease types, no relationship between rate of healing in paucibacillary patients and sulfone levels were found, and type of response in multibacillary patients and sulfone levels were unrelated. No substantial accumulation of the sulfones in the Karimui patients receiving continuous therapy with DADDS for 5 years was indicated from a comparison with the levels in the Filipino patients following a single injection of DADDS.