The stability testing of carbamazepine in spiked-saliva using HPLC-UV

The physicochemical characteristics of carbamazepine allow it to distribute to varied biological matrices, including saliva. The positive correlation between its concentration in saliva and in serum underlines the saliva as an alternative to biofluid matrices in carbamazepine bioanalysis in the interest of therapeutic drug monitoring (TDM). Carbamazepine stability testing becomes an essential part of TDM protocol to verify the absence of degradation throughout the whole process from analyte sampling to analysis. This study aimed to assess the stability of carbamazepine in spiked-saliva using HPLC-UV at 285 nm in diverse conditions. The analyte separation was done using the liquid-liquid extraction technique with chloroform, ammonia, and C8 stationary phase (4.6x150mm, 5µm). The results demonstrated that carbamazepine stock solution was stable in methanol solvent both at an ambient temperature and at 4°C, for corresponding 24 hours and 30 days. Carbamazepine also maintained its stability in spiked-saliva for up to 24 hours at an ambient temperature as well as after preparation. However, it became unstable when stored for a long period, even at -20°C, and after a freeze-thaw cycle. This study recommends that carbamazepine saliva concentration is examined within a maximum of 24 hours after sampling to continue providing accurate data for a consideration when making decision on dose adjustment or diagnosis of carbamazepine toxicity in clinical setting.