Abstracts

Rationale: Generic substitution of antiepileptic drugs (AEDs) may lead to adverse events and increased healthcare costs for patients with epilepsy. The objectives of this study were (1) to determine the switchback rates in AEDs compared to other therapeutic areas; (2) to investigate medical services utilization and economic impacts associated with generic switching of lamotrigine, the first new-generation AED to become generic in Canada.Methods: Medical and pharmacy claims data from Québec’s provincial health plan (RAMQ) database from 04/1998 and 07/2006 were used. Patients with epilepsy (ICD-9 345) and treated with branded lamotrigine for >60 days in the 90 days before generic entry were selected. An open-cohort design was used to classify patients into periods of branded versus generic use of lamotrigine. The switchback rate, defined as the proportion of patients who had switched to a generic drug but then switched back to the corresponding brand drug, were calculated for lamotrigine, and compared to other AEDs (clobazam, gabapentin, carbamazepin CR) and non-AED chronic-use drugs for the treatment of hypertension and hyperlipidemia (simvastatin, fosinopril, carvedilol). Periods of branded and generic use of lamotrigine were compared for medical resource utilization (frequency per person-year observed) and for total healthcare costs ($ per person-year observed), consisting of costs from prescription drugs, inpatient services and outpatient services. All costs were expressed in 2006 constant Canadian dollars.Results: 671 patients met the inclusion and exclusion criteria, corresponding to 1,650.9 and 291.2 person-years of branded and generic use of lamotrigine, respectively. A total of 187 (27.9%) branded lamotrigine patients switched to a generic version during the observation period, of whom 51 (27.5%) patients switched back to the brand lamotrigine. Rates of switchback ranged from 20.8% to 44.1% for AEDs and from 7.7% to 9.1% for non-AEDs. Multivariate analyses confirmed statistically significant lower generic switch rates and higher switchback rates among AEDs compared to other chronic-use drugs. Generic use periods showed higher mean daily dose of lamotrigine (251.4 vs. 239.1 mg, p=0.0149), higher incidence rates of medical services (9.8 versus 8.7 visits per person-year, p<0.0001), and longer hospital stays (4.86 vs. 3.29 days/person-year, p<0.0001) compared to brand use. An increase in overall health care costs was observed in the generic period compared to brand use ($7,902 vs. $6,419 per person-year, p=0.0128), despite the lower acquisition cost of generic lamotrigine. Medical service costs were 45% higher in the generic period ($4,389 vs. $3,028 per person-year, p=0.0131) than during the branded-use period.Conclusions: Use of generic lamotrigine in Quebec, Canada was significantly associated with increased physician visits, hospitalizations, and overall medical costs compared to branded use.