Direct observation of 3-keto-valproate in urine by 2D-NMR spectroscopy

Abstract

Background: It is known that valproate and its metabolites cause hepatotoxicity. The drug monitoring of valproate is important to determine an effective dose to keep an appropriate concentration in blood. Methods: In a 2-dimensional (2D)-NMR spectrum of double quantum filtered correlation spectroscopy (DQF-COSY), clear correlation peaks were ascertained to be due to 3-keto-valproate, which was a β-oxidation product of valproate. Results: A predominant metabolite of valproate was observed by proton NMR spectroscopy in the crude urine of a particular patient with metabolic disorder. The assignment of the signals was determined by synthesized 3-keto-valproic acid ethyl ester. The concentration of 3-keto-valproate in the urine was calculated to be 631 μg/mg creatinine by the integration of the peak of the isolated triplet methyl protons of C 5 at 1.016 ppm. Conclusion: Although the NMR spectra of crude urine of the patients who took valproate were usually complicated with many metabolites, the signals of 3-keto-valproate in a DQF-COSY spectrum of the urine of patients were easily connected according to the present assignment. The NMR analysis of the urine of patients who are prescribed valproate is useful for therapeutic drug monitoring and for checking the compliance of the patients.