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Clinical trials for the newer antiepileptic drugs (AEDs) have provided inconclusive information to evaluate comparative risk benefit. The authors use data from postmarketing observational cohort studies to compare the failure of treatment with lamotrigine, vigabatrin, and gabapentin in patients with refractory epilepsy. The Drug Safety Research Unit has conducted prescription event monitoring (PEM) studies for lamotrigine, vigabatrin, and gabapentin to monitor their safety when used in primary care. The primary outcome of this study was time to treatment failure in patients who had been prescribed the drug after the start of the PEM study. Patients on gabapentin had reduced time to treatment failure compared to those on the other 2 drugs. The age- and sex-adjusted hazard ratio of failure was 1.53 (95% confidence interval [CI] = 1.38–1.70) for gabapentin compared to lamotrigine and 1.19 (95% CI= 1.10–1.30) for vigabatrin compared to lamotrigine. The observed differences between the 3 study drugs might be confounded by a higher proportion of patients treated with gabapentin having refractory epilepsy, a shorter duration of the gabapentin PEM study, and a lower relative dose of gabapentin (approved at the time of the PEM study). The current study provides information about the routine usage of newer AEDs, which complements evidence from clinical trials regarding the efficacy and safety of these AEDs. Although this study showed differences on times to treatment failure between lamotrigine, vigabatrin, and gabapentin, the results are only useful when considered together with results from other studies seeking to answer the same questions.