Metabolism and interactions of antileprosy drugs.

Leprosy is a chronic infectious disease caused my Mycobacterium leprae that primarily affects peripheral nervous system and extremities and is prevalent in tropical countries. Treatment for leprosy with multidrug regimens is very effective compared to monotherapy especially in multibacillary cases. The three major antileprosy drugs currently in use are 4, 4'-diaminodiphenyl sulfone (DDS, dapsone), rifampicin, and clofazimine. During multidrug therapy, the potent antibiotic rifampicin induces the metabolism of dapsone, which results in decreased plasma half-life of dapsone and its metabolites. Furthermore, rifampicin induces its own metabolism and decreases its half-life during monotherapy. Rifampicin upregulates several hepatic microsomal drug-metabolizing enzymes, especially cytochrome P450 (CYP) family that in turn induce the metabolism of dapsone. Clofazimine lacks significant induction of any drug-metabolizing enzyme including CYP family and does not interact with dapsone metabolism. Rifampicin does not induce clofazimine metabolism during combination treatment. Administration of dapsone in the acetylated form (acedapsone) can release the drug slowly into circulation up to 75 days and could be useful for the effective treatment of paucibacillary cases along with rifampicin. This review summarizes the major aspects of antileprosy drug metabolism and drug interactions and the role of cytochrome P450 family of drug metabolizing enzymes, especially CYP3A4 during multidrug regimens for the treatment of leprosy.

Relapses in multibacillary patients treated with multi-drug therapy until smear negativity: findings after twenty years.

The Schieffelin Leprosy Research and Training Center at Karigiri, India participated in several of the World Health Organization (WHO) trials. The first trial on combined therapy in multi-bacillary leprosy was initiated in 1981. The main objectives of this field trial were to evaluate the efficacy of WHO recommended regimens in preventing relapses, especially drug resistance relapses. This paper reports on the relapses twenty years after patients were inducted into the WHO field trial. Between 1981 and 1982, 1067 borderline lepromatous and lepromatous patients were inducted into the WHO field trial for combined therapy in multi-bacillary leprosy trial. Among them, 357 patients were skin smear positive. During the follow-up in 2002, only 173 of them could be traced and assessed. The mean duration of follow-up was 16.4 +/- 1.83 years. Two patients relapsed 14 and 15 years after being released from treatment, the relapse rate being 0.07 per 100 person years follow-up. Drug susceptibility tests done on one of the relapsed patients revealed drug sensitive organisms to all multi-drug therapy drugs.

Activities of respository preparations of cycloguanil pamoate and 4,4'-diacetyldiaminodiphenylsulfone, alone and in combination, against infections with Plasmodium cynomolgi in rhesus monkeys.

The studies summarized in this report were concerned with the capacities of repository preparations of cycloguanil pamoate (CGT-P) to protect rhesus monkeys against infections with drug-susceptible and pyrimethamine-resistant strains of Plasmodium cynomolgi. Administered intramuscularly as a suspension in an oleaginous vehicle, CGT-P (i) provided long-term protection against single and repetitive challenges of rhesus monkeys with sporozoites of the drug-susceptible B and Ro strains, (ii) effected prompt clearance of parasitemia in established infections, and (iii) delayed relapse. Protection was equated to absence of parasites on thick blood films, negative results when blood was transferred to susceptible recipients, and inability to activate infection by splenectomy. Eventual loss of protection was not related to emergence of parasites resistant to cycloguanil (CGT). Although protection varied from monkey to monkey, its mean duration was related directly to size of CGT-P dose and size of particles in the suspension. Urinary excretion studies indicated that protection persisted as long as the daily output of CGT did not fall below that attained with the parenterally administered hydrochloride salt at a dose equivalent to 0.015 mg of CGT per kg. Studies on infections with the resistant Ro/PM strain showed that the activity of CGT-P was compromised severely by resistance to pyrimethamine. Attempts to minimize this liability by concomitant administration of 4,4'-diacetyldiaminodiphenylsulfone met with limited success. These results suggest that even the best of the repository preparations of CGT-P, with or without 4,4'-diacetyldiaminodiphenylsulfone, would be useful only in areas where Plasmodium falciparum and Plasmodium vivax are fully susceptible to chlorguanide and pyrimethamine.

A rabbit--in vitro system to evaluate drug action against Plasmodium falciparum.

A rabbit-in vitro model system is described which can determine the activity of anti-malarial drugs against erythrocytic stages of Plasmodium falciparum. Serum samples, collected from rabbits at various times after drug administration, wee incubated with synchronized ring form parasites using the microtest system. The extent to which the presence of drugs in the serum inhibited parasite growth was usually determined after 32 to 40 hours of incubation. Anti-malarial activity was observed in sera obtained from rabbits which received chloroquine, mefloquine, pyrimethamine and cycloguanil, but not in those which received 4-4' diacetyldiaminodiphenylsulphone (DADDS). The effects against the drug-sensitive strain were more marked than against the drug-resistant one. The serum activity persisted for a longer period of time after administration of mefloquine, pyrimethamine, pamoate, and cycloguanil pamoate than after administration of chloroquine, a drug with a shorter biological half-life. The results indicate that this model may be a useful system for identifying potential agents against drug-resistant falciparum malaria, particularly compounds which are converted in vitro to their active metabolites or which exert a prolonged suppressive activity after drug administration.