Topiramate (TPM) is a second-generation antiepileptic drug designed to treat epilepsy that can be prescribe alone or in combination with other medications. It is also used to treat migraine in adults and seizures associated with Lennox-Gastaut syndrome in children. Despite its frequent use, the metabolism of TPM has not yet been fully elucidated. To this end, a very sensitive and validated LC-MS/MS analytical method (quantification of metabolites down to 0.001 mg/L) was previously developed. This method enabled us to analyse the real plasma samples from 66 patients undergoing regular treatment for epilepsy with TPM and to evaluate the concentrations of TPM and its five metabolites. Before the analysis was carried out, the method was tested and adjusted and upgraded accordingly. The main purpose of the Master's thesis was to evaluate the importance of therapeutic monitoring of TPM. This required evaluating the effect of the sampling time, the effect of the daily dose of TPM and the effect of combined therapy with carbamazepine (CBZ) on plasma concentrations of TPM and its metabolites. The measured plasma sample concentrations in the steady state showed that there is a high variability in the concentration of TPM and its metabolites in patients receiving daily doses of TPM from 50 to 1200 mg. Although a trend can be observed between higher daily doses of TPM and a higher concentration of analytes, the correlation is rather poor. Similarly, when comparing patients who receive the same daily dose, the variability was significant, as the measured concentrations of the analytes varied up to 10-fold. Nevertheless, the dose of TPM has a significant effect on the concentration of TPM and its metabolites, while the sampling time only has a significant effect on plasma TPM concentration. TPM is mostly metabolized to 2,3-desizopropylidene TPM (ca. 100-fold higher concentration compared to other metabolites), followed by 10-hydroxy TPM and the other three metabolites (in the same size class). As for the use of TPM in conjunction with higher doses of CBZ (800-1600 mg/day), combined therapy has proven to have a significant effect on plasma TPM concentration, as the concentration of TPM decreases with the increase in the CBZ dose. Higher doses of CBZ also significantly increase the standardize value of two metabolites, with the effect being more pronounced for 2,3-desizopropylidene TPM. Based on the data collected and evaluated, we can confirm the hypothesis that therapeutic monitoring of TPM is essential for the safe and effective treatment of epilepsy.
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