Determination of carbamazepine profile in human plasma by GC-MS

Epilepsy is a major disease affecting millions of people worldwide. Carbamazepine is on the World Health Organization's list of essential medicines and is one of the most prescribed medicines for treating epilepsy. It has a narrow therapeutic range (4–12 μg/mL). Due to this narrow therapeutic range, toxic and adverse reactions are likely to be observed in the clinic. Therefore, therapeutic drug monitoring (TDM) should be routinely performed in the clinic for epilepsy patients treated with carbamazepine. Considering that an antiepileptic drug produces an antiepileptic effect only when its free (non-protein bound) concentration crosses the blood-brain barrier and reaches the brain, knowing and measuring the free drug fraction is important. In this study, a GC-MS method was developed for TDM of total and free carbamazepine, and carbamazepine epoxide in plasma. Free carbamazepine and carbamazepine epoxide were collected by ultra-filtrate, and analytes were extracted in plasma using salt-assisted liquid-liquid extraction (SALLME). The method was validated according to the European Medicines Agency (EMA) bioanalytical method validation guidelines. In the developed method, calibration curves were constructed for total carbamazepine, free carbamazepine, total carbamazepine epoxide, and free carbamazepine epoxide with calibration ranges of 1–20 µg/mL, 0.25–20 µg/mL, 0.4–8 µg/mL, and 0.1–8 µg/mL, respectively. The corresponding LLOQ values were 1, 0.25, 0.4, and 0.1 µg/mL. The correlation coefficient for both molecules was > 0.99 and the developing technique was applied to TDM for carbamazepine profile for plasma of patient samples.