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14-07-2011 | Cardiology | Article

Polypharmacy common in patients vulnerable to adverse drug events


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MedWire News: Almost 14% of patients vulnerable to adverse drug events were prescribed one or more high-risk drugs, a survey of general practices in Scotland has found.

The number of long-term drugs prescribed to patients is strongly associated with high-risk prescribing (HRP) but there is little evidence regarding the frequency of HRP or how it varies between patients and between practices.

To determine how common HRP is for patients vulnerable to adverse drug events, how reliably indicators can be used to measure a practice's rate of HRP, and which patient and practice characteristics are associated with HRP, a team led by Bruce Guthrie from the University of Dundee surveyed 315 general practices in Scotland.

The practices had 1.76 million registered patients, 139,404 of whom were vulnerable to adverse drug events because of age, comorbidity, or coprescription.

The researchers defined 15 individual indicators of HRP: four each for nonsteroidal anti-inflammatory drugs, coprescription with warfarin, and prescribing in heart failure, two for dose instructions for methotrexate, and one for antipsychotic prescribing in dementia.

The researchers tested how reliably each indicator and a composite of all 15 indicators could be used to identify whether a practice had an above or below average rate of HRP.

Of the patients particularly vulnerable to adverse drug events, 19,308 (13.9%) had received at least one HRP in the past year

Variation between practices in the rate of HRP was considerable. The reliability of the composite indicator for a median-sized practice was 0.92, with reliability greater than 0.7 in 95.6% of practices and greater than 0.8 in 88.2%.

"We can be reasonably confident that the composite indicator correctly defines practices as having above average or below average rates of HRP," comment the researchers.

In a multilevel logistic regression analysis, the patient characteristic most strongly associated with HRP was the number of drugs prescribed long term, with an odds ratio of 7.90 for patients prescribed more than 11 long-term drugs compared with patients prescribed no long-term drugs.

Writing in the BMJ, the researchers conclude: "HRP will often be appropriate, but the large variation between practices suggests opportunities for improvement."

MedWire ( is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011

By Joel Levy

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