Adverse drug reactions as cause of admission to hospital: prospective analysis of 18 820 patients.

OBJECTIVE: To ascertain the current burden of adverse drug reactions (ADRs) through a prospective analysis of all admissions to hospital.

DESIGN: Prospective observational study.

SETTING: Two large general hospitals in Merseyside, England.

PARTICIPANTS: 18 820 patients aged > 16 years admitted over six months and assessed for cause of admission.

MAIN OUTCOME MEASURES: Prevalence of admissions due to an ADR, length of stay, avoidability, and outcome.

RESULTS: There were 1225 admissions related to an ADR, giving a prevalence of 6.5%, with the ADR directly leading to the admission in 80% of cases. The median bed stay was eight days, accounting for 4% of the hospital bed capacity. The projected annual cost of such admissions to the NHS is 466m pounds sterling (706m Euros, 847m dollars). The overall fatality was 0.15%. Most reactions were either definitely or possibly avoidable. Drugs most commonly implicated in causing these admissions included low dose aspirin, diuretics, warfarin, and non-steroidal anti-inflammatory drugs other than aspirin, the most common reaction being gastrointestinal bleeding.

CONCLUSION: The burden of ADRs on the NHS is high, accounting for considerable morbidity, mortality, and extra costs. Although many of the implicated drugs have proved benefit, measures need to be put into place to reduce the burden of ADRs and thereby further improve the benefit:harm ratio of the drugs.