Background: Drug-drug interactions (DDIs) are responsible for a variety of adverse reactions, particularly in an elderly population.
Objective: To assess the frequency and potential clinical relevance of DDIs in a population aged > or = 55 years.
Methods: Exposure to DDIs was assessed in 7842 people participating in the Rotterdam Study, a population-based cohort study. These people were followed between 1 January 1992 and 1 July 2005. The DDI list of the Royal Dutch Association for the Advancement of Pharmacy, in which DDIs are categorized by potential clinical relevance and quality of evidence, was used. Simultaneous use of interacting drug combinations was calculated on the basis of drug dispensing data from community pharmacies.
Results: The incidence of a first dispensing of DDIs in the study period was 10.5 per 100 person-years and 2.7 per 100 person-years for potentially life-threatening DDIs. The prevalence of DDIs in people aged > or = 70 years increased from 10.5% in 1992 to 19.2% in 2005. Ten DDIs comprised two-thirds of the total exposure time to DDIs. The prevalence of potentially life-threatening DDIs in people aged > or = 70 years increased from 1.5% to 2.9%. This increase was most likely caused by an increase in use of spironolactone combined with renin-angiotensin-aldosterone system inhibitors.
Conclusion: A large number of people in the Netherlands aged > or = 55 years are exposed to DDIs and this number has increased sharply between 1992 and 2005. Healthcare professionals should pay special attention to the potential risks of DDIs in these people, particularly if spironolactone is involved.