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. 2010 Sep;88(3):347-53.
doi: 10.1038/clpt.2010.90. Epub 2010 Jul 14.

Refilling and switching of antiepileptic drugs and seizure-related events

J J Gagne  1 , J Avorn, W H Shrank, S Schneeweiss
Affiliations

Refilling and switching of antiepileptic drugs and seizure-related events

J J Gagne et al. Clin Pharmacol Ther. 2010 Sep.

Abstract

We sought to estimate the risk of seizure-related events associated with refilling prescriptions for antiepileptic drugs (AEDs) and to estimate the effect of switching between brand-name and generic drugs or between two generic versions of the same drug. We conducted a case-crossover study using health-care databases from British Columbia, Canada, among AED users who had an emergency room visit or hospitalization for seizure (index seizure-related event), defined using International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9) codes 345.xx (epilepsy and recurrent seizures) and 780.3x (convulsions), between 1997 and 2005. AED prescription refilling itself was associated with 2.3-fold elevated odds of seizure-related events when the refill occurred within 21 days before the index event (odds ratio (OR) 2.31; 95% confidence interval (CI) 1.56-3.44). The OR was 2.75 (95% CI 0.88-8.64) for refills that involved switching, yielding a refill-adjusted OR for switching of 1.19 (95% CI 0.35-3.99). Refilling the same AED prescription was associated with an elevated risk of seizure-related events whether or not the refill involved switching from a brand-name to a generic product.

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Figures

Figure 1
Figure 1
Case-crossover design to study the association between seizure-related outcomes and refilling and switching of antiepileptic medications. Note: In primary analyses, the induction period was defined as 1 day (i.e. day t-1) and 21 days were used for the case- (i.e. days t-22 to t-2) and the control-period (i.e. days t-43 to t-23).
Figure 2
Figure 2
Distributions of exposures (refills and switches) in the 8 weeks preceding the index event dates.
Figure 3
Figure 3
Results of sensitivity analyses (odds ratios and 95% confidence intervals) for the association between refilling or switching antiepileptic medications and seizure-related outcomes, along with difference in differences results, varying the case- and control-periods, the induction period, and the grace period.
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