Polypharmacy

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Our most complex patients are at highest risk for Drug-Drug Interactions. Polypharmacy, narrow therapeutic range of the medication, decreased hepatic and/or renal function of the patient each may increase the risk for DDIs. Each may be identified prior to coadministration. One should consider the potential for DDIs at all steps of the drug-delivery process. In a retrospective review of patients admitted to the emergency department, patients taking 3 or more medications or patients who were 50 years or older taking 2 or more medications had a considerable risk for DDIs. Furthermore, an increasing number of medications administered further increased the risk for adverse effects. Patients taking 2 medications had a 13% risk while patients taking 5 medications had a 38% risk for DDIs. Patients taking 7 or more medications had an 82% risk of developing adverse drug interactions.
Advanced age is an additional risk factor for DDIs. Aparasu and colleagues found that the risk for DDIs increases significantly after 44 years of age and is greatest for patients over 74 years of age. The need for multiple medications often arises with advancing age that may further the risk for DDIs. Almost 25% of the elderly outpatients referred to a diagnostic clinic in The Netherlands for decreased cognition, functional dependence, or both who were taking more than 1 medication were found to have potential adverse effects or decreased drug effect possibly due to a DDI. In general, when multiple medications are prescribed in the elderly population, the risk for DDIs increases exponentially.
Other patient-related risks for DDIs noted below, include very young age, female sex, genetics, decreased organ function, use of a medication having a narrow therapeutic range (eg, warfarin, digoxin, and cyclosporine), major organ impairment, metabolic or endocrine risk conditions (eg, hypothyroidism, hypoproteinemia), and acute medical issues (eg, dehydration).
Patient-Related Risks for Drug-Drug Interactions
  • Acute medical condition (eg, dehydration, infection);
  • Age extremes (ie, the very young and the elderly);
  • Decreased renal/ hepatic function;
  • Female sex;
  • Metabolic or endocrine condition (eg, obesity, hypothyroidism);
  • Multiple medication use;
  • Narrow therapeutic range of medication; and
  • Pharmacogenetics.

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