Background Medication is one of the major causes of adverse events in hospitalised patients.1 Of these so-called adverse drug events (ADEs), 15–60% is preventable.2 Surgical patients may be especially at risk for ADEs due to many inhospital transfers with medication related handovers. However, detailed information on the nature of surgical ADEs is lacking.

Purpose The aim of this study was to determine the incidence and nature of ADEs in surgical patients in order to evaluate the effect of future clinical pharmacy interventions on surgical ADEs.

Materials and methods This observational cohort study was conducted in eight surgical units of three Dutch hospitals. Elective surgical patients hospitalised for more than 48 h were included. A trigger tool tailored for the surgical population was developed to preselect medical records for potential ADEs. Causality, severity and preventability of ADEs were assessed by an independent expert panel of surgeons and clinical pharmacologists.

Results Medical records of 567 included patients (March–June 2009) were screened for triggers. Records (n=340) with one or more triggers were evaluated by the expert panel. They found 28 ADEs per 100 admissions of which a major part (75%) was classified as mild. Almost half of the ADEs was related to gastro-intestinal harm such as nausea. Particularly opioids (52%) were responsible for ADEs. Over 15% of the ADEs was judged preventable, of which 25% was classified as severe or life-threatening. Harm caused by anticoagulants accounted for 21% of the preventable ADEs.

Conclusions Surgical patients are indeed at risk for mainly mild ADEs. A quarter of the preventable ADEs is classified as severe or life-threatening. Major problems concern the use of opioids and anticoagulants. The results of this study provide enough evidence that the pharmaceutical care in surgical patients can be improved. The effect of clinical pharmacy interventions on surgical ADEs is now being evaluated.3