DETERMINATION OF MK-507, A NOVEL TOPICALLY EFFECTIVE CARBONIC-ANHYDRASE INHIBITOR, AND ITS DE-ETHYLATED METABOLITE IN HUMAN WHOLE-BLOOD, PLASMA, AND URINE BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Sensitive methods for the determination of a novel topically effective carbonic anhydrase inhibitor (CAI) I, MK-507, and its de-ethylated me tabolite II, in human whole blood, plasma and urine were developed. Th ese methods were based on liquid-liquid extraction of I and II from bi ological matrices, back extraction into acid, and analysis by high-per formance liquid chromatography (HPLC) with ultraviolet (UV) detection (252 nm). The assays were fully validated in the concentration range o f 5 to 500 ng/ml, and the limit of quantification (LOQ) for I and II, defined as the lowest concentration on the standard curve for which pr ecision (coefficient of variation, C.V.) is < 10%, was 5 ng/ml in whol e blood, plasma, and urine. These methods were applied for the analyse s of biological fluid samples from a variety of clinical pharmacokinet ic studies. In addition, a method in whole blood based on column-switc hing HPLC with UV detection and with an LOQ of 50 ng/ml was also devel oped. The switching valve was used to eliminate interferences from lat e eluting peaks extracted from whole blood. The details of these assay s, together with some representative data from a human study, are pres ented.