Interchangeability among carbamazepine formulations: the impact over epilepsy patients

ABSTRACT

Abstract The treatment of epilepsy is complex and a matter of concern is the interchangeability among different formulations available for antiepileptic drugs. To evaluate the effects of interchangeability among carbamazepine formulations on patients with epilepsy. This is a prospective cohort study that included adult outpatients diagnosed with epilepsy and under pharmacological treatment with carbamazepine. Before switching the brand/manufacturer, the "Interchangeable Pharmaceutical Product in the Treatment of Epilepsies" questionnaire was applied. The questionnaires "Adverse Events Profile" and Quality of Life in Epilepsy-31, so as the plasma carbamazepine concentrations, were evaluated before and after the brand/ manufacturer switch. Physical-chemical tests aiming to assess tablets quality were performed in accordance with the Brazilian Pharmacopoeia 5th edition. The study population was composed by 14 patients (mean age 44.6 years), with 10 of females. From those interviewed, 10 had no knowledge about the three antiepileptic drugs formulations available. The frequency of adverse event "problems with skin" incresead (p=0.023) and "upset stomach" decreased (p=0.041) after the changeover. The adverse events profile was associated with only two quality of life domains "energy/fatigue" (p=0.048) and "total score" (p=0.018). Divergent results between generic and reference formulations were observed in purity-water test (reference 1.96%, generic 4.84%) and dissolution test, in which the generic formulation presented 66.27 to 85.77% of carbamazepine dissolved after the third level. Conclusions: Objective differences before and after the brand/manufacturer switch were not observed, in spite of patients' perceptions. Despite that, more studies in the field are necessary, especially on the interchangeability among generic antiepileptics, in order to better elucidate switching consequences on patients' life.