The risks and costs of multiple-generic substitution of topiramate

• Published in: Neurology Vol. 72; no. 24; p. 2122
• Main Authors: Duh, M S, Paradis, P E, Latrémouille-Viau, D, Greenberg, P E, Lee, S P, Durkin, M B, Wan, G J, Rupnow, M F T, LeLorier, J
• Format: Journal Article
• Language: English
• Published: United States 16.06.2009
• Subjects: Adult; Anticonvulsants - administration & dosage; Anticonvulsants - adverse effects; Anticonvulsants - economics; Chronic Disease - drug therapy; Cohort Studies; Comorbidity; Craniocerebral Trauma - epidemiology; Dose-Response Relationship, Drug; Drug Administration Schedule; Drug Costs - statistics & numerical data; Drug Costs - trends; Drug Utilization - economics; Drugs, Generic - administration & dosage; Drugs, Generic - adverse effects; Drugs, Generic - economics; Epilepsy - drug therapy; Epilepsy - epidemiology; Female; Fractures, Bone - epidemiology; Fructose - administration & dosage; Fructose - adverse effects; Fructose - analogs & derivatives; Fructose - economics; Health Benefit Plans, Employee - economics; Health Care Costs - statistics & numerical data; Health Care Costs - trends; Hospitalization - statistics & numerical data; Humans; Insurance, Health, Reimbursement - economics; Male; Patient Acceptance of Health Care; Proportional Hazards Models; Quebec; Retrospective Studies; Risk Factors; Quebec
• ISSN: 1526-632X
• DOI: 10.1212/WNL.0b013e3181aa5300

To investigate clinical and economic consequences following generic substitution of one vs multiple generics of topiramate (Topamax; Ortho-McNeil Neurologics, Titusville, NJ). Medical and pharmacy claims data of Régie de l'Assurance-Maladie du Québec from January 2006 to October 2007 were used. Patients with epilepsy treated with topiramate were selected. An open-cohort design was used to classify the observation period into periods of brand, single-generic, and multiple-generic use. One-year generic-switch and switchback-to-brand rates were estimated using Kaplan-Meier methodology. Medical resource utilization and costs were compared among the three periods using multivariate regression analysis. In total, 948 patients were observed during 1,105 person-years of brand use, 233 person-years of single-generic use, and 92 person-years of multiple-generic use. A total of 23% of generic users received at least two different generic versions. Compared to brand use, multiple-generic use was associated with higher utilization of other prescription drugs (incidence rate ratio [IRR] = 1.27, 95% confidence interval [CI] = 1.24-1.31), higher hospitalization rates (0.48 vs 0.83 visit/person-year, IRR = 1.65, 95% CI = 1.28-2.13), and longer hospital stays (2.6 vs 3.9 days/person-year, IRR = 1.43, 95% CI = 1.27-1.60), but the effect was less pronounced in single-generic use (hospitalization: IRR = 1.08, 95% CI = 0.88-1.34, length of stay: IRR = 1.12, 95% CI = 1.03-1.23). The risk of head injury or fracture was nearly three times higher (hazard ratio = 2.84, 95% CI = 1.24-6.48) following a generic-to-generic switch compared to brand use. The total annualized health care cost per patient was higher in the multiple-generic than brand periods by C$1,716 (cost ratio = 1.21, p = 0.0420). Multiple-generic substitution of topiramate was significantly associated with negative outcomes, such as hospitalizations and injuries, and increased health care costs.