Background Drug interactions (DIs) are a significant cause of medication-related problems. The aging population, high chronic diseases prevalence and polypharmacy are closely associated factors. Aim of the review To study the prevalence, types and associated factors of DIs in multimorbidity patients of over 65 years of age in primary care. Methods Relevant studies on DI prevalence in this population were reviewed in PubMed, Cochrane Library and EMBASE (January 2000-December 2015). Independent variables (duration, target population, age, sex, mean of drugs and diseases, geographical localization, DI databases used and study designs) and dependent variables (prevalence, number of DIs per 100 patients and per patient, number of clinically-relevant DIs per 100 patients, most common DI and associated factors) were classified for each article. Results The search generated 749 articles and 46 duplicates were discarded. After reviewing, 10 articles were included. Seven studies were observational and 3 were quasi-experimental. Seven out of 10 used interaction databases. Only 2 studies described both actual and potential DIs. The prevalence of multimorbidity patients with DI ranged from 25.1 to 100% and the number of DIs per 100 patients was from 30 to 388.3. All the lower values correspond to the study conducted at the nursing home. This could be due to special care offered in these centres, where the medication is more controlled. The most frequent DIs were reported in five articles. However, these results could not be correlated since they were ranked using different methodologies. ACEIs, diuretics and NSAID were the most common therapeutic groups. Finally, 5 studies identified factors associated with the presence of potential DIs. The number of drugs and age were the most significant factors. Conclusions There is little evidence of prevalence of actual and potential DIs in elderly patients with multimorbidity in outpatient settings, showing widely heterogeneous results.
Keywords: Aged; Drug interaction; Outpatients; Patients with multimorbidity; Prevalence.