Driving forces behind increasing cardiovascular drug utilization: a dynamic pharmacoepidemiological model

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT center dot Several studies indicate that switch to more expensive drugs and increasing treatment intensity, rather than population ageing have been responsible for rising drug expenditures during the 1990s. center dot Little is known about the driving forces behind the increasing treatment intensity with cardiovascular drugs. WHAT THIS STUDY ADDS center dot This study provides a new pharmacoepidemiological method to analyse drug utilization trends, applying dispensing data at the individual level. center dot The suggested semi-Markov model allows for quantification of the influence of changing incidence, discontinuation and user mortality on rising treatment prevalence. center dot Increasing treatment incidence was the main driver behind rising treatment prevalence for most cardiovascular drug categories. center dot Whereas declining discontinuation drove some of the growth, declining mortality among drug users had little influence. To investigate the driving forces behind increasing utilization of cardiovascular drugs. Using register data, all Danish residents as of 1 January 1996 were followed until 2006. Cohort members were censored at death or emigration. Cardiovascular drug utilization on the individual level was traced, applying registered out-of-hospital dispensing. The impact of population ageing on cardiovascular drug utilization was investigated using standardized intensities and prevalences. Based on a three-state (untreated, treated and dead) semi-Markov model, we explored to what extent increasing treatment prevalence was driven by changing incidence, discontinuation and mortality. Expected treatment prevalences were modelled, applying stratum-specific cohort prevalence in 1996 along with incidence, discontinuation and drug user mortality either throughout 1996-2004 or at fixed 1996 levels. Treatment prevalence (ages >= 20 years) with cardiovascular drugs increased by 39% during 1996-2005 from 192.4 to 256.9 per 1000 inhabitants (95% confidence interval 256.5, 257.3). Treatment intensity grew by 109% from 272 to 569 defined daily doses 1000(-1) day(-1). Population 'middle-ageing' accounted for 11.5 and 20.3%, respectively. Increasing treatment incidence was the main driver of the rising treatment prevalence in most drug categories. Declining discontinuation drove some of the growth, declining drug user mortality less. Even with fixed incidence in the model, treatment prevalence continued to increase. Age-related increases in treatment intensity and prevalence, rather than population ageing, drove the increasing treatment intensity with cardiovascular drugs. Increasing treatment prevalence in subgroups was primarily caused by increasing incidence. Due to pharmacoepidemiological disequilibrium, treatment prevalence will continue to grow even with unchanged incidence.