Projected economic impact of clinical findings of generic entry of topiramate on G4 European countries

Curr Med Res Opin. 2009 Jul;25(7):1793-805. doi: 10.1185/03007990903044374.


Objectives: To explore the effects of generic substitution of the antiepileptic drug (AED) topiramate (Topamax) in Canada; to convert observed Canadian costs into the settings of France, Germany, Italy, and the United Kingdom (UK); and to forecast the economic impact of generic topiramate entry in these four European countries.

Design and methods: Health claims from Régie de l'assurance maladie du Québec (RAMQ) plan (1/2006-9/2008) and IMS Health data (1998-2008) were used. Patients with epilepsy and > or = 2 topiramate dispensings were selected. An open-cohort design was used to classify observation into mutually-exclusive periods of branded versus generic use of topiramate. Canadian healthcare utilization and costs (2007 CAN$/person-year) were compared between periods using multivariate models. Annualized per-patient costs (2007 euro or 2007 pound sterling/person-year) were converted using Canadian utilization rates, European prices and service-use ratios. Non-parametric bootstrap served to assess statistical significance of cost differences. Topiramate market was forecasted following generic entry (09/2009-09/2010) using autoregressive models based on the European experience. The economic impact of generic topiramate entry was estimated for each country.

Results: A total of 1164 patients (mean age: 39.8 years, 61.7% female) were observed for 2.6 years on average. After covariates adjustment, generic-use periods were associated with increased pharmacy dispensings (other AEDs: +0.95/person-year, non-AEDs: +12.28/person-year, p < 0.001), hospitalizations ( + 0.08/person-year, p = 0.015), and lengths of hospital stays (+0.51 days/person-year, p < 0.001). Adjusted costs, excluding topiramate, were CAN$1060/person-year higher during generic use (p = 0.005). Converted per-patient costs excluding topiramate were significantly higher for generic relative to brand periods in all European countries (adjusted cost differences per person-year: 706-815 euro, p < 0.001 for all comparisons). System-wide costs would increase from 3.5 to 24.4% one year after generic entry.

Limitations: Study limitations include the absence of indirect costs, possible claim inaccuracies, and IMS data limitations.

Conclusions: Higher health costs were projected for G4 European countries from the Canadian experience following the generic entry of topiramate.

Publication types

  • Comparative Study
  • Evaluation Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Anticonvulsants / economics
  • Anticonvulsants / therapeutic use
  • Canada
  • Child
  • Child, Preschool
  • Drugs, Generic / economics*
  • Drugs, Generic / therapeutic use*
  • Europe
  • European Union / economics*
  • Female
  • Forecasting
  • Fructose / analogs & derivatives*
  • Fructose / economics
  • Fructose / therapeutic use
  • Health Care Costs
  • Health Resources / statistics & numerical data
  • Humans
  • Male
  • Middle Aged
  • Retrospective Studies
  • Topiramate
  • Young Adult


  • Anticonvulsants
  • Drugs, Generic
  • Topiramate
  • Fructose