Liquid chromatography–tandem mass spectrometric assay for clobetasol propionate in human serum from patients with atopic dermatitis

A bioanalytical assay for the topical corticosteroid clobetasol propionate was developed and validated. For the quantitative assay 0.5 ml human serum samples, supplemented with clobetasone butyrate as internal standard, were extracted with hexane–ether. Evaporated and reconstituted extracts were injected on a polar embedded octadecyl silica column with isocratic elution using formic acid in water–methanol as mobile phase. The eluate was led into the electrospray interface with positive ionization and the analyte was detected and quantified using the selective reaction monitoring mode of a triple quadrupole mass spectrometer. The assay was validated in the range 0.04–10 ng/ml, the lowest level of this range being the lower limit of quantification. Precisions were 5–10% and accuracies were between 102 and 109%. The drug was stable under all relevant conditions. Finally, the assay was successfully applied on patients suffering from severe atopic dermatitis treated topically with clobetasol propionate.