A high-performance liquid chromatography method for the determination of carbamazepine and carbamazepine-10,11-epoxide and its comparison with chemiluminescent immunoassay.

BACKGROUND

Carbamazepine is a first-choice antiepileptic drug for the treatment of simple and complex partial seizures. The use of an established therapeutic range for carbamazepine concentration is limited by the presence of carbamazepine-10,11-epoxide, its active metabolite that significantly contributes to the efficacy and toxicity and is not routinely measured and accounted for. This article describes the development of a HPLC method for determination of carbamazepine and carbamazepine-10,11-epoxide in serum, and compares it with chemiluminescence immunoassay to evaluate the importance of considering the active metabolite in therapeutic strategies.

METHODS

The procedure involves protein precipitation, separation on a reverse-phase column and ultraviolet detection. The analytical procedure proved to be sensitive, selective, precise, accurate and linear (regression coefficients >0.999) in the range of 0.5-25.0 microg/mL and 0.1-10.0 microg/mL for quantification of carbamazepine and carbamazepine-10,11-epoxide, respectively. For the comparison between methods, serum samples of 75 patients using the medication were evaluated.

RESULTS

The Pearson correlation coefficient showed that the carbamazepine concentrations measured by HPLC are significantly higher than those obtained by immunoassay (mean difference of 1.07 microg/mL, 95% limits of agreement from -0.65 to 2.80 microg/mL).

CONCLUSIONS

This difference may be decisive for the therapy. In some cases, this may affect the individual dosage adjustment and subsequent treatment.