Therapeutic drug monitoring (TDM) of anti-epileptic drugs (AED) is a routine application. Carbamazepine (CRB) is monitored as the parent drug while oxcarbazepine (OXC) and eslicarbazepine acetate (ESL) are monitored as their active metabolite (eslicarbazepine; MHD). We have developed a UPLC-MS/MS method for determining CRB, OXC, ESL and MHD in plasma or serum with a simplified extraction protocol. The developed method detects sildenafil (SLD), which clinically interferes with AED and is likely to be co-administered in epileptic patients suffering from sexual insufficiency (60%). MHD was prepared in-house. AED were simultaneously determined in presence of SLD using gatifloxacin as an internal standard (IS). Separation was achieved using acetonitrile, methanol and 100 mm ammonium acetate in water (32:3:65, v/v/v) on an Intersil® RP-HPLC column (250 × 4.6 mm, 5 μm). A one-step extraction was performed by simultaneous protein and phospholipids precipitation. Detection was done by tandem mass spectrometry. No relative matrix effect was observed. The method was linear (0.5-40 μg/mL for CRB, ESL and MHD and 0.05-4 μg/mL for OXC), accurate and selective. Recoveries were 64.41 ± 5.07, 45.62 ± 1.73, 61.41 ± 4.77 and 60.33 ± 1.36 for CRB, OXC, ESL and MHD, respectively. The method was successfully applied for TDM of AED.
Keywords: anti epileptic drus; dose adjustment; drug-drug interaction; eslicarbazepine; oxcarbazepine; removal of phospholipids.
Copyright © 2016 John Wiley & Sons, Ltd.