Economic impact of generic substitution of lamotrigine: projected costs in the US using findings in a Canadian setting.

BACKGROUND

Generic substitution may not always save health care costs for antiepileptic drugs (AED).

OBJECTIVE

(1) To examine the economic impacts of generic substitution of lamotrigine in Canada; and (2) to convert observed Canadian costs to a United States (US) setting.

METHODS

Health claims from Québec's health plan (RAMQ) between 08/2002 and 07/2006 were analyzed. Patients with > or = 1 epilepsy claim and treated with branded lamotrigine (Lamictal) before generic entry were selected. Health care costs ($/person-year) were compared during periods of branded and generic use of lamotrigine. Two cost-conversion methods were employed; one using purchasing power parities, US/Canada service use ratios, and exchange rate, and another employing Canadian health care utilization and US unit costs.

RESULTS

671 patients were observed during 1650.9 and 291.2 person-years of branded and generic use of lamotrigine, respectively. The generic-use period was associated with an increase in overall costs (2006 constant Canadian dollars) relative to brand use (C$7902 vs. C$6419/person-year; cost ratio (CR) = 1.22; p = 0.05), despite the lower cost of generic lamotrigine. Non-lamotrigine costs were 33% higher in the generic period (p = 0.013). Both conversion methods yielded increases in total projected health care costs excluding lamotrigine (2006 constant US dollars) during the generic period (Method 1: cost difference: US$1758/person-year, CR = 1.33, p = 0.01); Method 2: cost difference: US$2516, CR = 1.39, p = 0.004).

LIMITATIONS

Study limitations pertain to treatment differences, indicators used for conversion and possible claim inaccuracies.

CONCLUSION

Use of generic lamotrigine in Canada was significantly associated with increased overall medical costs compared to brand use. Projected overall US health care costs would likely increase as well.