Determination of isotretinoin or etretinate and their major metabolites in human blood by reversed-phase high-performance liquid chromatography

A method is described for the quantitative analysis of isotretinoin and its 4-oxo metabolite, or of etretinate and its principal metabolites, in human blood in the range 10-2000 ng/ml. Following a simple one-step extraction, the compounds are determined by reversed-phase high-performance liquid chromatography (HPLC) with gradient elution and detection at 365 nm. This highly specific method separates the cis and trans isomers of the parent compounds and their metabolites. Examples are given of the application of this method to clinical studies of these two therapeutically important retinoids.