Adverse drug reaction-related hospitalizations in persons aged 55 years and over: a population-based study in The Netherlands

Background: Elderly individuals appear to be particularly at risk of developing adverse drug reactions (ADRs) because of higher rates of polypharmacy, age-related pharmacokinetic changes, pharmacodynamic variations and substantial co-morbidity levels. Thus, the increasing contribution of elderly individuals to the total population means ADR-related hospitalizations are expected to become more frequent. However, a recent study conducted in the Netherlands found that ADR-related hospitalizations had stabilized during the years 1997-2007. Nonetheless, this study did not take into account the number of medicines used. Objectives: Therefore, the objectives of this study were to describe the association between age and sex, and the risk of an adverse drug reaction (ADR)-related hospitalization in persons aged 55 years and over in the Netherlands and to correlate these ADR-related hospitalizations with the number of dispensed medicines over the same period. Methods: Data on hospital admissions were obtained from the Dutch nationwide registry of hospital discharges. Data from Statistics Netherlands were used to obtain population demographics. Data on dispensed medicinal products were obtained from the Dutch Foundation for Pharmaceutical Statistics. Analyses were performed by calculating relative risks (RRs). Results: Those aged ≥75 years were at a more than 4-fold increased risk of being hospitalized in comparison with those aged 55-64 years (RR 4.15; 95% CI 4.12, 4.18). In addition, female sex was associated with an increased risk of an ADR-related hospitalization (RR 1.05; 95% CI 1.03, 1.08) in comparison with males. When taking into account the number of dispensings, elderly ≥75 years of age were at an increased risk of being hospitalized for an ADR due to anticoagulants (RR 2.20; 95% CI 2.12, 2.28), antidiabetic agents (RR 3.53; 95% CI 3.39, 3.66), salicylates (RR 1.70; 95% 1.54, 1.86) and antirheumatics (RR 2.19; 95% CI 2.06, 2.33). Conclusion: In our study, we showed that elderly aged ≥75 years were at increased risk of an ADR-related hospitalization. Given that the number of elderly and very old will continue to grow, it is of pivotal importance to further endorse drug safety in this vulnerable patient group.