Binding of centchroman with human serum as determined by charcoal adsorption method

Protein binding of drugs is an important factor influencing both pharmacoki netic and pharmacodynamic parameters. Thus, knowing the extent of protein b inding of drugs is crucial. Centchroman is a non-steroidal once a week oral contraceptive. It has been reported to be useful for the treatment of brea st cancer and osteoporosis. Ample data has been generated on pharmacokineti cs of centchroman in animals and humans. The extent of protein binding of c entchroman has not been established so far. Non-specific adsorption of the drug limits the use of conventional methods like ultrafiltration and equili brium dialysis. A method of charcoal adsorption as reported by Yuan et al. (method I) was used after modification (method II) to determine its binding to human serum. The extent of protein binding (%) is estimated from declin e of percent drug remaining in the supernatant after adding the charcoal. S tudy was carried out at 1- and 10-mu g/ml concentrations in drug free human serum samples and an HPLC assay was used to determine concentration-time d ata. The percentage of centchroman remaining in serum versus time data was analysed using non-linear fitting programs on WinNonlin software. Method II was found to give higher estimates of protein binding than the former meth od by preventing the dilution effect. Using this method, the extent of prot ein binding of centchroman was found to be 101.83 +/- 1.28 and 94.87 +/- 3. 59% at 1 and 10 mu g/ml, respectively. However, it was similar to 90% in th e individual serum samples showing intersubject variability in protein bind ing of centchroman. (C) 1999 Elsevier Science B.V. All rights reserved.