Abstracts

Rationale: According to the US Food and Drug Administration (FDA), “A-rated” compounds are considered to be therapeutically bioequivalent to the reference-listed drug, even though plasma concentrations may vary by up to 25%. Surveys and case reports suggest that some epilepsy patients may encounter health problems when switching between distinct product formulations. The objectives of the study were to compare the medication history of two groups: 1) epileptic patients with evidence of an inpatient, emergency department, or ambulance treatment claim (defined as an event); and 2) epileptic patients with no evidence of an event. Methods: This study was a case-control analysis using a large retrospective claims repository of US health plan data (PharMetrics claims from January 2005- June 2007). Cases and controls were identified by a primary diagnosis code for epilepsy (ICD-9 of 345.xx). Cases were further identified based upon the existence of a claim for any of the 3 types of defined treatment events. Both groups received anticonvulsant medications for at least 145 days within 6 months prior to an index date. We compared the odds ratios of an event between patients who had a medication change between A-rated generic alternatives for an anticonvulsant medication (defined as a switch) and those who did not. Results: A total of 11,360 patients met the study criteria (991 cases, 10,369 controls). When controlling for age, sex, region of the country, and type of seizure diagnosis, the odds ratio of the occurrence of an event between those who switched medication and those who did not was 1.91 (CI = 1.53 to 2.39). In addition, a propensity score calculation was conducted to select 991 matched controls for the case group. When performing a logistic regression using the same variables as above, only switching was still a significant predictor of an event (odds ratio = 1.45; CI = 1.04 to 1.93). Conclusions: This analysis found an association between patients receiving epilepsy care in an emergency department, ambulance, or inpatient setting and the prior occurrence of formulation switching involving A-rated anti-epileptic generic medications.