Liquid chromatographic assay for fluoxymesterone in human serum with application to a preliminary bioavailability...

Fluoxymesterone was extracted from serum with a liquid-liquid extraction procedure. Serum containing both drug and internal standard, 6 alpha-methylprednisolone, was extracted with methylene chloride. The extract was washed with 0.1 M NaOH and water, evaporated, and reconstituted with mobile phase. Chromatography was performed on a Zorbax Sil column, preceded by a guard column, with a mobile phase composed of 50% water-saturated butyl chloride:tetrahydrofuran:methanol:phosphoric acid (880:100:15:0.5). Fluoxymesterone and methylprednisolone were detected by UV absorption at 236 nm. Overall recovery was 80%. Calibration curves were linear for fluoxymesterone concentrations from 5 to 100 ng/mL. The assay is accurate and precise (RSD values less than or equal to 7%); endogenous steroids did not interfere with the assay. Assay suitability was assessed in a bioavailability study in which six subjects each received two treatments of 10-mg fluoxymesterone tablets in a Latin-square crossover study. The two treatments were a tablet administered either buccally or orally. Cmax values ranged from 40 to 150 ng/mL with tmax values of 1-2 h. The harmonic mean half-life of fluoxymesterone was 2.0 h. Less than 8% of the AUC was extrapolated. Mean Cmax and AUC values from the oral treatment were 80 and 76%, respectively, of the mean values from the buccal treatment.