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

BMJ 2004; 329 doi: (Published 01 July 2004) Cite this as: BMJ 2004;329:15
  1. Munir Pirmohamed, professor of clinical pharmacology1 (munirp{at},
  2. Sally James, research pharmacist3,
  3. Shaun Meakin, research nurse2,
  4. Chris Green, senior pharmacist2,
  5. Andrew K Scott, consultant in care of the elderly3,
  6. Thomas J Walley, professor of clinical pharmacology1,
  7. Keith Farrar, chief pharmacist3,
  8. B Kevin Park, professor of pharmacology1,
  9. Alasdair M Breckenridge, professor of clinical pharmacology1
  1. 1 Department of Pharmacology and Therapeutics, University of Liverpool, Liverpool L69 3GE
  2. 2 Royal Liverpool University Hospital, Liverpool L7 8XP
  3. 3 Wirral Hospitals NHS Trust, Wirral CH49 5PE
  1. Correspondence to: M Pirmohamed
  • Accepted 11 June 2004


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 (€706m, $847m). 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.


  • We thank June Raine (MHRA) for her encouragement and assistance with this study, all staff in both hospitals who assisted with the study, and, in particular, S Roberts, S Morrison-Griffiths, and R Brady for their help in identifying case notes and in data extraction.

  • Contributors MP, TJW, BKP, and AMB devised the idea of the study, while MP and AMB raised funding. MP oversaw the whole study. SJ and SM collected the data and input the data into databases. AKS, CG, and KF were responsible for study implementation, and review and supervision of the data collection in hospital B; MP and AMB undertook the same roles in hospital A. The analyses were carried out independently by MP and SJ, and verified by TJW. MP produced the first draft, and all authors contributed to the final draft of the manuscript. MP is guarantor for the study.

  • Funding The study was funded by the MHRA (Medicines and Healthcare Products Regulatory Agency; formerly the Medicines Control Agency). The MHRA had no role in data interpretation or in the production of this manuscript.

  • Competing interests At the time of the study, AMB was chairman of the Committee on Safety of Medicines and now is chairman of the MHRA. MP is a member of the Committee on Safety of Medicines and of the subcommittee on pharmacovigilance. BKP is a member of the Committee on Safety of Medicines.

  • Ethical approval Liverpool Local Research Ethics Committee and Wirral Health Authority Research Ethics Committee.

  • Accepted 11 June 2004
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