Abstracts

Carbamazepine (CBZ) is a first-line therapy for the treatment of epilepsy. Extended-release delivery systems may offer important advantages, including potentially reducing peak-related neurotoxicity improveing adherence. We examined the patterns of pharmacotherapy, rates of serious adverse events, and the utilization and costs for patients treated with the available CBZ formulations.
Data were retrieved from the PharMetrics Patient-Centric Database for 2,738 patients who were diagnosed with epilepsy and started on Carbatrol, Tegretol XR, Tegretol, or generic carbamazepine between July 1999 and June 2001. Patients who were previously on carbamazepine therapy, had incomplete data records, or had a pre-existing adverse event were excluded. Patient demographic and clinical characteristics, serious adverse events, discontinuations, CBZ therapy switches, and utilization and costs for related care subsequent to treatment initiation were recorded. Annual rates of adverse events and discontinuations were calculated and the risks of these events were compared across cohorts using Cox proportional hazards models controlling for pretreatment and/or demographic differences.
Using Carbatrol as the reference group, there was no statistically significant difference in the risk of serious adverse events among the treatment groups (hazard ratio [HR]: Carbatrol, 1.00; Tegretol XR, 0.97; Generic CBZ, 1.06). A lower percentage of subjects switched off extended-release CBZ relative to immediate-release CBZ (Carbatrol, 5.0%; Tegretol XR, 5.2%; generic CBZ, 14.8%; Tegretol, 17.5%). Proportional hazards regression analysis for time to discontinuation by initial anti-epileptic therapy revealed a significant difference between extended-release formulations and generic CBZ (HR: Carbatrol, 1.00; Tegretol XR, 1.05; Generic CBZ, 1.38; [italic]P[/italic][lt].001). Payments for epilepsy related healthcare services at one year were lower for Carbatrol (although not statistically significantly) relative to the other cohorts (Carbatrol, $2,462 [plusmn] $265; Tegretol XR, $2,674 [plusmn] $253; Tegretol $3,197 [plusmn] $396; generic CBZ $3,053 [plusmn] $377).
Among the available CBZ formulations, this study found no significant differences in the rate of serious adverse events. Epilepsy-related costs were lower for extended-release formulations, but the differences did not reach statistical significance. However, the rate of discontinuation of therapy was significantly lower for extended-release formulations and patients switched off extended-release carbamazepine at a lower rate relative to generic CBZ. More studies are needed to determine why patients are more likely to continue taking extended-release CBZ relative to immediate-release formulations.
[Supported by: Study funded by an unrestricted grant by Shire US Inc.]