Chromatographic separation of vigabatrin, gabapentin and pregabalin on porous graphitic carbon: Application in therapeutic drug monitoring

The antiepileptic drugs vigabatrin, gabapentin and pregabalin are of polar and hydrophilic nature, and thus difficult to retain on reversed phase stationary phases. In our study, we present the chromatographic separation of these substances on porous graphitic carbon as stationary phase by gradient elution using 0.1% trifluoroacetic acid and acetonitrile as mobile phases. Sample preparation from human plasma consisted of addition of the stable isotope labelled internal standard D₄-pregabalin, dilution by 0.1% trifluoroacetic acid and protein precipitation by perchloric acid. Extraction efficiency was quantitative with no significant differences to 100% theoretical yield. The analytes were detected by tandem mass spectrometry. Selectivity was very good with no signals observed from endogenous substances nor other potentially co-administrated antiepileptic drugs. Calibration ranges were 0.5-25 μg/mL, 0.6-30 μg/mL and 0.2-10 μg/mL for vigabatrin, gabapentin and pregabalin, respectively, and covered the therapeutic concentrations of these substances in human plasma. Precision of the method was better than 10% for all analytes at all concentration levels, while accuracy was better than 15% at the LLOQ and better than 10% at all other levels. The method was successfully introduced in our laboratory for routine TDM in patients treated with these drugs.