Determination of carbamazepine and its main metabolite carbamazepine-10, 11-epoxide in rat brain microdialysate and blood using ESI-LC-MS (ion trap)

A new analytical method has been developed and validated for determination of the anti-epileptic drug carbamazepine (CBZ) and its main metabolite carbamazepine- 10, 11 -epoxide (CBZ-E) using ESl-LC-MS (ion trap). The compounds were separated on a C18 (150 x 2.1 mm I.D., 3 pm particles) column and were isocratically eluted in the mobile phase consisting of water-acetonitrile-acetic acid (74.5:25:0.5, v/v) using the flow rate of 0.4 mL min(-1). The other anti-epileptic drug oxcarbamazepine (OXC) was used as an internal standard. The retention times for CBZ-E, OXC and CBZ were 5.6, 6.8, 12.8 min. Signals of the compounds were monitored under multi-reaction monitoring mode (MRM) of ESl-LC-MS (ion trap) for the quantification. Selected ions of CBZ-E, OXC and CBZ in MRM were m/z 253 -> 210, m/z 253 -> 180 and M/z 237 -> 194. The method was validated over the concentration range of 5.0-500.0 ng mL(-1) and was applied to rat brain microdialysate and blood samples for the determination of CBZ and main metabolite. The brain microdialysate and the blood sample were collected simultaneously after intra-peritoneal injection of CBZ (12 mg kg(-1)) during a period of 10 h. No interference from endogenous substances and matrix effect were found on the separation of microdialysates and blood samples. The consequent signals of the compounds were resolved and integrated clearly. The LC-MS method was presented as an alternative to investigate pharmacokinetic parameters of CBZ and CBZ-E in blood and brain studies.