Objective: The aim of this study was to assess the impact of removing prior-authorization restrictions on the use of thiazolidinediones (TZDs) and outcomes.
Methods: In a controlled interrupted time-series analysis, whereby new users of antidiabetic agents over 65 years of age in adjacent Canadian provinces with different TZD-related policies [Alberta (n=16,653) and Saskatchewan (n=6682)] were followed from January 2001 to December 2006. Prior authorization for TZDs was removed in Alberta (intervention province) in December 2003 (rosiglitazone) and February 2004 (pioglitazone); no policy changes occurred in Saskatchewan (control province). Adjusted differences in percent change between intervention and control provinces were used to estimate policy-attributable effects (PAE) on TZD use within 30 days and 1 year and patient outcomes (composite of all-cause mortality or hospitalization for acute coronary events or heart failure) within 1 year.
Results: Mean age was 75 years, 51% were female, and 206,055 antidiabetic prescriptions were dispensed during follow-up. TZD use within 30 days among new users of antidiabetic agents increased almost >10% in Alberta compared with Saskatchewan controls immediately following the policy change: PAE=9.4%, 95% confidence interval, 7.3%–11.6%. Other less expensive antidiabetic drug use decreased to exactly the same extent, suggesting TZD substitution. Compared with the controls, in Alberta there were no changes in the primary (clinical) composite outcome at 1 year (PAE=0.31%, 95% confidence interval, −2.8% to +3.4%).
Conclusions: The removal of a prior-authorization policy for TZDs was associated with an immediate increase in TZD use but did not impact patient outcomes. In this case, the policy removal shifted drug use to a more expensive drug with less certain clinical benefit.