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Polypharmacy as commonly defined is an indicator of limited value in the assessment of drug-related problems.
Viktil, Kirsten K. 1,3; Blix, Hege S. 2,3; Moger, Tron A. 4; Reikvam, Aasmund 3
[Miscellaneous Article] British Journal of Clinical Pharmacology. 63(2):187-195, February 2007.

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What is already known about this subject:

* Polypharmacy has been linked to heightened risk of occurrence of drug-related problems (DRPs) and a detrimental health outcome.

* Polypharmacy has been variously defined; in research studies a commonly applied definition has been the concomitant use of five or more drugs.

* The value of using a definite number of drugs as a cut-off to describe polypharmacy as a risk factor for the occurrence of DRPs has not been validated.

What this study adds:

* Nearly half of the patients admitted to general hospitals used five or more drugs; during the hospital stay these patients were prescribed as many new drugs as those admitted with fewer drugs.

* The presence of DRPs increased approximately linearly with the number of drugs used, for the range of one to >11 drugs.

* To set a strict cut-off to identify polypharmacy and declare that using more than this number of drugs represents a potential risk for occurrence of DRPs, is of limited value in clinical practice.

Aim: To investigate whether polypharmacy defined as a definite number of drugs is a suitable indicator for describing the risk of occurrence of drug-related problems (DRPs) in a hospital setting.

Methods: Patients admitted to six internal medicine and two rheumatology departments in five hospitals were consecutively included and followed during the hospital stay, with particular attention to medication and DRPs. Comparisons were made between patients admitted with five or more drugs and with less than five drugs. Clinical pharmacists assessed DRPs by reviewing medical records and by participating in multidisciplinary team discussions.

Results: Of a total of 827 patients, 391 (47%) used five or more drugs on admission. Patients admitted with five or more and less than five drugs were prescribed the same number of drugs after admission: 4.1 vs. 3.9 drugs [P= 0.4, 95% confidence interval (CI) - 0.57, 0.23], respectively. The proportion of drugs used on admission which was associated with DRPs was similar in the patient group admitted with five or more drugs and in those admitted with less than five drugs. The number of DRPs per patient increased approximately linearly with the increase in number of drugs used; one unit increase in number of drugs yielded a 8.6% increase in the number of DRPs (95% CI 1.07, 1.10).

Conclusion: The number of DRPs per patient was linearly related to the number of drugs used on admission. To set a strict cut-off to identify polypharmacy and declare that using more than this number of drugs represents a potential risk for occurrence of DRPs, is of limited value when assessing DRPs in a clinical setting.