Valproic acid intoxication identified by1H and1H-13C correlated NMR spectroscopy of urine samples

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

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 beta-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 microg/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.

Identification and quantitation of xenobiotics by 1H NMR spectroscopy in poisoning cases

In order to analyse a wide range of xenobiotics and their metabolites present in biological fluids, NMR spectroscopy can be used. A large variety of xenobiotics (therapeutic agents, pesticides, solvents, alcohols) can be characterized and quantitated directly, without sample preparation. NMR investigations were applied to acute poisoning cases, involving drugs such as salicylates and valproic acid (VPA). In a salicylate poisoning case, the three major metabolites of acetylsalicylic acid have been detected in crude urine, and rapid identification of lysine revealed the origin of the intoxication, namely lysine acetylsalicylate (Aspegic). Valproic acid as its glucuronide was identified in urine samples from two poisoned patients. 1H NMR was also used to identify and quantitate paraquat (Gramoxone) in urine owing to its two aromatic signals at 8.49 and 9.02 ppm, in two acutely poisoned patients (183 and 93 mg/l). An intentional poisoning case with tetrahydrofuran (THF) was also investigated. Serum and urine samples were collected. THF was characterized by its resonances at 1.90 and 3.76 ppm, and quantified at 813 and 850 mg/l in the two biological fluids, respectively. Moreover, two other compounds were detected: lactate and gamma-hydroxybutyric acid (GHB). 1H NMR spectroscopic analysis of serum samples from three poisoned patients revealed methanol in one case and ethylene glycol in the two others. Moreover, in the same spectrum, the corresponding metabolites formate and glycolate were found. Compared with the reference chromatographic or spectrophotometric methods, requiring time-consuming extraction and/or derivatization steps, NMR spectroscopy allows the determination of many exogenous and endogenous compounds, without any pre-selection of the analytes.