Factors affecting drug interactions and their clinical importance in geriatric outpatients

Introduction: Polypharmacy can lead to drug-drug interactions. The aim of this study was to determine the possible factors affecting the prevalence and clinical importance, and interrater reliability of clinical significance of drug interactions in geriatric outpatients. Materials and Method: Potential drug-drug interactions in 228 patients treated in an outpatient geriatric clinic were evaluated in this cross-sectional, retrospective study. The potential significance of the interactions was reviewed separately by a geriatrician and a clinical pharmacist. Results: A total of 1342 drugs were prescribed (median 6 [2-14], per patient). Mean age of the patients was 78±0.5 (65-96). Polypharmacy was present in 64.0% of the patients. A weak positive correlation was found between patient age and the number of drugs used (Rs =.205; p=.002). No drug interaction was detected in 18.0% of the patients. In the prescriptions of the remaining 187 patients 760 category C, 70 category D, and 18 category X interactions (Lexicomp®) were detected. A strong positive correlation was found between the number of drugs per patient and the number of drug interactions (Rs =.734; p<.001). There was a strong correlation between the number of interactions and the presence of polypharmacy (rpb=.702, p<.001). The measure of agreement between the clinicians was more pronounced for category D and X interactions (Cohen’s k=.714 and 1, p<.001). Conclusion: Advanced age, a higher frequency of concomitant use of drugs, and polypharmacy are factors that require clinicians to be aware of drug-drug interactions. Clinical pharmacists can work with geriatricians in outpatient clinics to prevent drug interactions. Keywords: Drug Interactions; Polypharmacy; Health Services for the Aged; Pharmacist.