Abstracts

Rationale: Since generic drugs are priced lower than their branded counterparts, a common misperception is that generic substitution lowers the health care cost. While this may lower the drug cost, we postulate that it may not always lead to an overall cost saving in the health care system, especially for narrow therapeutic index (NTI) medications such as antiepileptic drugs (AED), due to the broad bioequivalence standard for generic approvals. The questionable clinical equivalence between generic and branded AEDs may result in a higher seizure recurrence risk and consequently higher health care utilization and cost. Previously we reported the economic impact of generic substitution of lamotrigine in Canada. The objective of this study is to convert observed Canadian costs to a United States (US) setting.Methods: Health claims data from Québec’s provincial health plan (RAMQ) between 08/2002 and 07/2006 were analyzed. Patients with ≥1 claim for epilepsy and treated with branded lamotrigine (Lamictal®) for ≥60 days of the 90 days prior to generic entry were selected. Periods of branded and generic use of lamotrigine were compared for total health care costs (CAD $ per person-year of observation), stratified into prescription drugs, inpatient services and outpatient services. Two different methods of cost conversion from the Canadian to US settings were used. The first method converted the observed Canadian costs using purchasing power parities, US over Canada service use ratios, and the Canada-US dollar exchange rate. The second conversion method started with the Canadian utilization of pharmacy and medical services, which were multiplied by the appropriate US over Canada service use ratios and by US unit costs. All costs were expressed in 2006 constant US dollars.Results: 671 patients formed the study population with 1,650.9 and 291.2 person-years of branded and generic use of lamotrigine, respectively. Method 1 yielded a 10.0% increase in total projected health care costs during the generic over the brand period (US$693 per person-year, p=0.064), while Method 2 showed an expected 8.9% increase (US$787 per person-year, p=0.020). In both cases, the lower cost of generic lamotrigine versus its branded counterpart (–US$1,175 in Method 1, –US$1,926 in Method 2; both p<0.001) was more than offset by the higher costs of other pharmacy utilization and medical services (Method 1: US$1,868, p=0.009; Method 2: US$2,713, p=0.006). Both projected US increases were lower than the observed Canadian increase (23.1%), due to the larger US price difference between brand and generic drugs compared to Canada, and to the relatively lower health care utilization in the US.Conclusions: The projected overall US health care costs would increase by 8.9%-10% when patients with epilepsy are switched from branded to generic lamotrigine. Whether this observed increase in costs will occur following the entry of other generic versions of newer AEDs on the US market is an issue that should be closely monitored.