Determination of medrogestone in plasma by high-performance liquid chromatography.

Interference with the UV absorbance of medrogestone by endogenous steroids in plasma was prevented by reacting plasma with oxalyl chloride. The reduction of interference was effective when oxalyl chloride was in the range 10-50 microl/ml plasma. Reaction of oxalyl chloride with plasma for 10 min could reduce interference approximately 5.5-fold, and there was no significant reduction after 30 min. The limit of quantitative concentration for medrogestone in HPLC was 1 ng/ml. The standard curves were linear with the correlation coefficient greater than 0.999 in the range of 1-30 ng/ml. The coefficients of variation of both intra- and inter-day mean values were <12% and <10% of the actual values, respectively. The developed method for plasma sample preparation and the evaluated HPLC condition were further applied to an in vivo pharmacokinetic study.