A drug-drug interaction (DDI) is defined as a pharmacokinetic or pharmacodynamic influence of drugs on each other, which may result in undesired effects such as reduced effectiveness or increased toxicity [1]. According to the Food and Drug Authority, drug-drug interactions occur when two or more drugs react with each other and this may make the interacting drugs less effective, cause unexpected side effects or increase the action of a particular drug [2]. Different drugs are often used concurrently with others to achieve a desired therapeutic goal and treat coexisting diseases or multi-morbidity conditions [3]. The presence of multi-morbidity increases the possibility of patients using many drugs concurrently, and this is associated with a high risk of potential drug-drug interactions [4, 5]. The concurrent use of many drugs (4 or more) is referred to as polypharmacy [6].
DDIs can be classified into two main groups i.e., pharmacokinetic DDIs and pharmacodynamic DDIs. Pharmacokinetic DDIs involve interference with the absorption, distribution, metabolism and excretion of one drug by another, whereas pharmacodynamic DDIs may be due to: direct effect of a drug on function of the receptor of another, interference with a biological or physiological control process and additive/opposed pharmacological effect of one drug on another. The toxic effects of DDIs may be adverse drug events that can be severe enough to necessitate hospitalization and increase hospital stay. Drug-drug interactions may also lead to poor health outcomes, as well as increased costs and utilization of healthcare service [7, 8].
In all health care systems, there is need for information on the occurrence of potential DDIs, knowledge of their associated factors and tools to identify them. These assist prescribers and other members of healthcare teams in predicting, identifying, and managing potential drug-drug interactions so as to minimize damages caused by them [9].
There are several factors that contribute to the occurrence of potential DDIs, including the number of medications prescribed at any given time, therapeutic drug classes in prescriptions, the patient's gender, age, number of prescribers involved, the presence of comorbidities, coinfections, and the availability of potential DDI identification tools [10].
From real-world data, there is proof of high prevalence of potential drug-drug interactions worldwide. Nearly 74,000 emergency room visits and 195,000 hospitalizations in the USA every year are caused by drug-drug interactions, resulting from the ineffectiveness of current approaches to DDI identification [11, 12].
Similarly, overall prevalence of potential DDIs in developing countries is high, ranging from 23–86% according to reports from hospital settings in Uganda, Ethiopia, Pakistan and Iran. Additionally, Uganda has a high overall prevalence of potential DDIs of 89.3% [13]. According to a study conducted by Lubinga and Uwiduhaye in 2011, 23% of in-patient prescriptions in Mbarara Regional Referral Hospital had potential DDIs [7].
Shortage of information concerning DDIs in resource-limited countries like Uganda results in more DDI related damage than in developed countries [14]. Despite understanding the role played by DDIs in therapeutic outcomes, there was limited information regarding their prevalence in outpatient settings in Uganda. To the best of our knowledge, the prevalence of potential DDIs in Southwestern Uganda was last documented in a 2008 study on inpatients at Mbarara Regional Referral Hospital. There was no study that explored potential DDIs in outpatient settings in Mbarara city. This study aimed to determine the prevalence, severity, and factors associated with potential drug-drug interactions in outpatient settings in Mbarara city.