Intended for healthcare professionals


Comorbidity and repeat admission to hospital for adverse drug reactions in older adults: retrospective cohort study

BMJ 2009; 338 doi: (Published 07 January 2009) Cite this as: BMJ 2009;338:a2752
  1. Min Zhang, senior research fellow,
  2. C D’Arcy J Holman, professor of public health,
  3. Sylvie D Price, research associate,
  4. Frank M Sanfilippo, research fellow,
  5. David B Preen, senior research fellow,
  6. Max K Bulsara, associate professor of biostatistics
  1. 1School of Population Health, University of Western Australia, Perth, WA, Australia
  1. Correspondence to: M Zhang min.zhang{at}
  • Accepted 1 October 2008


Objectives To identify factors that predict repeat admission to hospital for adverse drug reactions (ADRs) in older adults.

Design Population based retrospective cohort study.

Setting All public and private hospitals in Western Australia.

Participants 28 548 patients aged ≥60 years with an admission for an ADR during 1980-2000 followed for three years using the Western Australian data linkage system.

Results 5056 (17.7%) patients had a repeat admission for an ADR. Repeat ADRs were associated with sex (hazard ratio 1.08, 95% confidence interval 1.02 to 1.15, for men), first admission in 1995-9 (2.34, 2.00 to 2.73), length of hospital stay (1.11, 1.05 to 1.18, for stays ≥14 days), and Charlson comorbidity index (1.71, 1.46 to 1.99, for score ≥7); 60% of comorbidities were recorded and taken into account in analysis. In contrast, advancing age had no effect on repeat ADRs. Comorbid congestive cardiac failure (1.56, 1.43 to 1.71), peripheral vascular disease (1.27, 1.09 to 1.48), chronic pulmonary disease (1.61, 1.45 to 1.79), rheumatological disease (1.65, 1.41 to 1.92), mild liver disease (1.48, 1.05 to 2.07), moderate to severe liver disease (1.85, 1.18 to 2.92), moderate diabetes (1.18, 1.07 to 1.30), diabetes with chronic complications (1.91, 1.65 to 2.22), renal disease (1.93, 1.71 to 2.17), any malignancy including lymphoma and leukaemia (1.87, 1.68 to 2.09), and metastatic solid tumours (2.25, 1.92 to 2.64) were strong predictive factors. Comorbidities requiring continuing care predicted a reduced likelihood of repeat hospital admissions for ADRs (cerebrovascular disease 0.85, 0.73 to 0.98; dementia 0.62, 0.49 to 0.78; paraplegia 0.73, 0.59 to 0.89).

Conclusions Comorbidity, but not advancing age, predicts repeat admission for ADRs in older adults, especially those with comorbidities often managed in the community. Awareness of these predictors can help clinicians to identify which older adults are at greater risk of admission for ADRs and, therefore, who might benefit from closer monitoring.


  • We thank the Data Linkage Branch, WA Department of Health, in particular, Diana Rosman, manager, for her assistance.

  • Contributors: MZ and CDJH devised the idea of the study, designed the methods, and raised funding. MZ was responsible for implementing the study and carrying out all the analyses. CDJH supervised the whole study. The following authors assisted in developing and verifying the study components: SDP for the hospital morbidity dataset; FMS for drug categories, modifications to the drug categories between coding systems, and drug dosing investigation; and DBP for comorbidity and ADR hospital episodes. MKB provided statistical advice. MZ prepared the first draft of the manuscript and all authors contributed to each section of the final draft of the manuscript. MZ is guarantor.

  • Funding: MZ is supported by a postdoctoral fellowship from the National Health and Medical Research Council (Australia).

  • Competing interests: None declared.

  • Ethical approval: This work was approved by the human research ethics committee of the University of Western Australia.

  • Provenance and peer review: Not commissioned; externally peer reviewed.

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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