• drug interactions;
  • hospitalisation;
  • hospital emergency service



Our objective was to evaluate the incidence of adverse patient outcomes due to drug–drug interactions (D–DIs), the type of drugs involved and the underlying reason. As a proxy for adverse patient outcomes, emergency department (ED) visits, hospital admissions and re-hospitalisations were assessed.


A literature search in the Medline and Embase database (1990–2006) was performed and references were tracked. An overall cumulative incidence was estimated by dividing the sum of the cases by the sum of the study populations.


Twenty-three studies were found assessing the relationship between D–DIs and ED-visits, hospitalisations or re-hospitalisations. The studies with a large study size showed low incidences and vice versa. D–DIs were held responsible for 0.054% of the ED-visits, 0.57% of the hospital admissions and 0.12% of the re-hospitalisations. In the elderly population, D–DIs were held responsible for 4.8% of the admissions. Drugs most often involved were NSAIDs and cardiovascular drugs. The reasons for admissions or ED-visits, which were most often found were GI-tract bleeding, hyper- or hypotension and cardiac rhythm disturbances.


This review provides information on the overall incidence of D–DIs as a cause of adverse patient outcomes, although there is still uncertainty about the impact of D–DIs on adverse patient outcomes. Our results suggest that a limited number of drugs are involved in the majority of cases and that the number of reasons for admission as a consequence of D–DIs seems to be modest. Copyright © 2006 John Wiley & Sons, Ltd.