Polypharmacotherapy and drug-drug interactions in patients hospitalized in an Internal Medicine department: magnitude of the problem and clinical implications

BACKGROUND The use of multiple drugs is a growing problem in elderly patients: it increases the risk of drug-drug interactions and reduces the compliance to cures. The magnitude and the clinical implications of this phenomenon in patients hospitalized in Internal Medicine departments (IM) remain largely unknown.
AIM OF THE STUDY To evaluate how frequently polypharmacotherapy occurs in IM patients, to what extent the hospitalization affects it, and to what extent potential drug-drug interactions have to do with the treated conditions.
MATERIALS AND METHODS In this observational study, the clinical records of 232 consecutive patients (median age 80 years) were reviewed, and the medical prescriptions on admission to and at discharge from the hospital were analysed, with special regard to potential drugdrug interactions, using the Micromedex® Healthcare Series system (www.thomsonhc.com); the interactions were classified in terms of severity and type (clinical relevance).
RESULTS The total number of prescribed drugs per-patient on admission and at discharge were 4.73 ± 2.88 vs 5.69 ± 2.78 (p < 0.01); the number of potentially harmful interactions were 0.91 ± 1.17 vs 1.39 ± 1.59 (p < 0.01); the percentage of patients at risk for any interactions (mostly moderate or severe, as a matter of fact) were 53% vs 66% (p < 0.01). As for clinical relevance, most interactions were of the pharmacodymanic type (67 vs 93, p n.s.), and very few patients (5 vs 5) had interactions potentially interfering with their disease status. The risk of interactions progressively increased with the number of prescribed drugs, reaching a plateau of 60% with the combination of 4 drugs.
CONCLUSIONS Our data confirm that drug-drug interactions due to polypharmacotherapy are a relevant problem in patients hospitalized in IM, and that hospitalization per se adds to its magnitude. Although few patients seem to be directly threatened in their disease status, most of them are exposed to the risk of multiple adverse effects, the reduction of which needs to be aimed at by the prescribing physicians.