Purpose: The aim of the study was to investigate preferential initiation with the two most frequently used statins, simvastatin and atorvastatin, by patient characteristics over time.
Methods: Statin initiators without a statin prescription during the 365 days preceding the initiation from 1 January 1998 through 31 December 2004 were captured from the nation-wide Prescription Register in Finland. Associations of demographic factors and morbidities with atorvastatin versus simvastatin at initiation of statin treatment were analysed by a logistic regression model adjusted for significant covariates separately for each year.
Results: Of all new statin users in 1998, atorvastatin was chosen for 18% and simvastatin for 39%. In 2004, the corresponding figures were 32 and 38%. Atorvastatin was more likely than simvastatin to be initiated in younger age groups than in persons older than 74 years (reference group). Initiation with atorvastatin was less likely for people with than without coronary artery disease; adjusted odds ratios ranged from 0.62 to 0.73 over the years 1998-2003.
Conclusion: Channelling of atorvastatin over simvastatin toward the younger and healthier population was found during the first 4 years after its launch in Finland. Channelling may lead to confounding by indication, which must be taken into account when designing pharmacoepidemiology studies on statins.