Background Adverse drug reactions (ADR) cause considerable morbidity and mortality.

Methods This 4-week study was undertaken in Cork University Hospital, Ireland, for all admissions from the emergency department (ED). A panel independently reviewed patients with suspected ADRs. Causality assessment was performed using the Naranjo ADR probability scale and the Hallas criteria was used to assess preventability of the ADRs.

Results During the study period, 1258 patients were admitted from the ED; of these, 856 patients were included in the study; 75 patients (8.8%) had an ADR-related admission. Over half were deemed to be ‘possibly’ or ‘definitely’ avoidable. The level of agreement between reviewers using the Naranjo and Hallas criteria was very low.

In the ADR group (n=75), 50.7% were men compared with 53.1% in the non-ADR group (n=781). The median age for patients in the ADR group was 73 years compared with 45 years in the non-ADR group. The average number of prescribed drugs per patient in the ADR group was 7.5 (SD±3.8) compared with 2.4 (SD±3.6) in the non-ADR group. Classified by drug type, 74.2% of the ADRs were attributed to cardiovascular and central nervous system drugs.

Conclusions This study estimated the incidence of ADR-related admissions to an Irish hospital at 8.8%, with 57.3% of these deemed to have been potentially avoidable. Older patients were more likely to have an ADR-related admission. Prescribers must be aware of this increased likelihood of an ADR when prescribing new drugs to this patient population, and regularly review treatment.