An improved gas chromatographic determination of valproic acid and valpromide in plasma.

A newly, improved analytical method for determination of valproic acid (VPA) and valpromide (VPD) in human plasma was developed. The method is based on gas chromatographic determination with flame ionization detection, after chloroform extraction of the drugs from plasma. Caprylic acid was used as an external standard. With the extraction procedure chosen, high recoveries for both VPA and VPD were achieved (98-102%), with correlation coefficient of 0.9998 for VPA and 0.9996 for VPD. Sensitivity of the method was also high (2 ng or 2 mg/L), while the linearity was obtained over the range of 5-150 mg/L, with high correlation for both drugs (0.9997 and 0.9995 for VPA and VPD, respectively). Reproducibility of the method was documented with low values of coefficients of variation, both inter-assay and day-to-day values (1.4-4.4 and 1.7-3.7 for VPA and 2.1-5.0 and 2.6-5.1 for VPD, respectively). The method has been used to follow VPA plasma levels in adult epileptic patients on sodium valproate therapy.