Clinical evidence of pharmacokinetic changes in thalidomide therapy.

The teratogenic effects of thalidomide have been studied for more than 50 years. However, there have been few studies of the pharmacokinetic changes occurring during thalidomide therapy. Thalidomide was originally developed as a sedative. However, thalidomide induces multiple birth defects when used in pregnant women. Thalidomide is now used in the treatment of multiple myeloma (MM) and erythema nodosum leprosum (ENL) in Japan. Rational use of thalidomide is problematic due to a lack of basic research regarding its mechanism of action and serum concentration/effect relationships. There are a number of hypotheses for pharmacokinetic changes in thalidomide therapy. Genetic factors including single nucleotide polymorphisms (SNPs) that change cytochrome P450 (CYP) activity and epigenetic regulation that modifies CYP expression levels may contribute to the changes in pharmacokinetics and adverse drug reactions (ADRs) of thalidomide. Environmental factors include the pharmacological context of drug-drug interactions and the physiological context of liver diseases. Liver and kidney diseases do not play important roles in pharmacokinetic changes or ADRs in thalidomide therapy. To date, most research has focused on teratogenic activity, while the impact of polymorphisms in genes encoding drug metabolic enzymes and drug-drug interactions could mediate ADRs. Here, we discuss clinical evidence of pharmacokinetic changes in thalidomide therapy.

Biowaiver monographs for immediate release solid oral dosage forms: rifampicin.

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of new multisource and reformulated immediate release (IR) solid oral dosage forms containing rifampicin as the only Active Pharmaceutical Ingredient (API) are reviewed. Rifampicin's solubility and permeability, its therapeutic use and index, pharmacokinetics, excipient interactions and reported BE/bioavailability (BA) problems were taken into consideration. Solubility and absolute BA data indicate that rifampicin is a BCS Class II drug. Of special concern for biowaiving is that many reports of failure of IR solid oral dosage forms of rifampicin to meet BE have been published and the reasons for these failures are yet insufficiently understood. Moreover, no reports were identified in which in vitro dissolution was shown to be predictive of nonequivalence among products. Therefore, a biowaiver based approval of rifampicin containing IR solid oral dosage forms cannot be recommended for either new multisource drug products or for major scale-up and postapproval changes (variations) to existing drug products.

Pharmacokinetics and relative bioavailability of clofazimine in relation to food, orange juice and antacid.

BACKGROUND: Clofazimine is potentially useful for the treatment of disease due to multidrug resistant Mycobacterium tuberculosis, as well as leprosy and certain chronic skin diseases. Its pharmacokinetics have been incompletely characterized. This study was conducted to explore issues relating to bioavailability in the presence of food, orange juice, and antacid. METHODS: A 5 drug regimen consisting of clofazimine, cycloserine, ethionamide, para-aminosalicyclic acid, and pyridoxime was administered to healthy subjects four times using a four period cross-over design with two weeks washout between treatments. Subjects also received orange juice, a high fat meal, aluminum/magnesium antacid, or only water in random order with the drug regimen. The pharmacokinetics of clofazimine were assessed using individual- and population-based methods and relative bioavailability compared to fasting administration was determined. RESULTS: Clofazimine exhibited a sometimes prolonged and variable lag-time and considerable variability in plasma concentrations. From the population analysis (one-compartment model), the mean oral clearance was 76.7 l/h (CV=74.2%) and mean apparent volume of distribution was 1470 l (CV=36.3%). The first-order absorption rate constant ranged from 0.716 to 1.33 h(-1) (pooled CV=61.7%). Residual (proportional) error was 49.1%. Estimates of bioavailability compared to fasting administration were 145% (90% CI, 107-183%) for administration with high fat food, 82.0% (63.2-101%) for administration with orange juice, and 78.5% (55.1-102%) for administration with antacid. CONCLUSION: Administration of clofazimine with a high fat meal provides the greatest bioavailability, however, bioavailability is associated with high inter- and intra-subject variability. Both orange juice and aluminum-magnesium antacid produced a reduction in mean bioavailability of clofazimine.