The rapid hydrolysis of chlordiazepoxide to demoxepam may affect the outcome of chronic osmotic minipump studies.

In chronic studies, the classical benzodiazepine chlordiazepoxide (CDP) is often the preferred drug because, unlike other benzodiazepines, it is soluble in water. However, rapid CDP hydrolysis in solution has been described. This would diminish plasma levels in chronic minipump studies and introduce the corelease of active compounds. Therefore, the present study aimed to explore the putative hydrolysis of CDP in aqueous solution over time and to identify the hydrolysis products. Moreover, we aimed to characterize the hydrolysis products for their in vitro (3H-flunitrazepam binding and oocyte electrophysiology) and in vivo (stress-induced hyperthermia paradigm) GABAA receptor potency. CDP in solution hydrolyzed to the ketone structure demoxepam which was confirmed using mass spectrometry. The hydrolysis was concentration dependent (first-order kinetics) and temperature dependent. CDP exerted greater potency compared to demoxepam in vitro (increased activity at GABAA receptors containing α1 subunits) and in vivo (stress-induced hyperthermia), although 3H-flunitrazepam binding was comparable. The classical benzodiazepine CDP is rapidly hydrolyzed in solution to the active compound demoxepam which possesses a reduced activity at the GABAA receptor. Chronic studies that use CDP in aqueous solution should thus be interpreted with caution. It is therefore important to consider drug stability in chronic minipump applications.