Background: An increase of therapeutic substitution after patent expiry might have a negative effect on cost-savings generated with newly introduced generic drugs. To evaluate influences of patent expiry on therapeutic substitution, switch behaviour before and after patent expiry was investigated.
Aim: To describe proton pump inhibitor use and investigate substitution patterns from omeprazole before and after patent expiry.
Methods: Data were obtained from the InterAction DataBase. Proportional proton-pump inhibitor use was identified per quarter during the study period 2000-2003. For the second part two cohorts--one before and one after patent expiry--were defined. The number of switchers was quarterly identified during 2-year follow-up period. For statistical analyses the chi-square test and hazard ratio were used.
Results: In proportional use, a downward trend for omeprazole was found. After patent expiry, significantly more patients switched to other proton pump inhibitors (P < 0.001). The hazard ratio of 0.62 (95% CI: 0.57-0.69), indicates that for every six patients switching before patent expiry, 10 patients switch after patent expiry.
Conclusion: After patent expiry more patients switch to another proton pump inhibitor. In light of the total savings achieved with generic omeprazole, the importance of this negative impact on total cost-savings on proton pump inhibitors is unclear.