Differential pulse polarographic assay procedure andin vitro biopharmaceutical properties of dipotassium clorazepate

Abstract

A differential pulse polarographic (DPP) assay was developed to measure the stability kinetics of dipotassium clorazepate at 37°C in various aqueous buffers and in whole blood, and to characterize its transfer across the everted intestinal sac preparation. Employing a differential extraction procedure along with DPP, it was possible to quantify dipotassium clorazepate and desmethyldiazepam, its major degradation product, and qualitatively identify a minor degradation product, 2-amino-5-chlorobenzophenone. The in vitro stability data indicate that the rate of degradation decreases with an increase in pH, with relatively instantaneous breakdown below pH 4 and relative stability at pH 7.4. Permeability across the everted sac preparation at pH 1.5 reflects instantaneous degradation and transfer of the degradation product, desmethyldiazepam. At pH 7.4, negligible desmethyldiazepam is formed and transferred across the sac preparation. In addition, the permeability profile of intact dipotassium clorazepate suggests a potential for permeability rate limited intestinal absorption. Overall, the data suggest that if dipotassium clorazepate is administered so that it bypasses the more favorable acidic pH environment for biodegradation, one should anticipate variable absorption, physiological disposition, and clinical profiles as a function of route of administration and dosage form.