Potential drug–drug interactions in internal medicine wards in hospital setting in Pakistan

Background Multiple drugs therapies may be the potential source of drug–drug interactions that can result in alteration of therapeutic response and/or increase untoward effects of many drugs. Objective To identify the frequency and levels of potential drug–drug interactions (pDDIs) in internal medicine wards and their association with patients’ age, gender, length of hospital stay and number of prescribed medications; and to describe management of frequently identified major or moderate pDDIs. Setting Internal medicine wards of two major tertiary care hospitals of Khyber Pakhtunkhwa, Pakistan. Method Micromedex Drug-Reax system was used to screen patient’s profiles for pDDIs. Logistic regression was applied to determine the odds ratio for specific risk factors of pDDIs i.e., age, gender, hospital-stay and number of medications. Main outcome measure Overall prevalence and prevalence of contraindicated, major, moderate and minor pDDIs; levels of pDDIs; frequently identified major or moderate interactions; and odds ratios for risk factors. Results Total, 188 interacting drug-combinations were identified that contributed to 675 pDDIs. Of 400 patients, 52.8 % patients were presented with at least one pDDI (overall prevalence), 21.3 % with at least one major-pDDI, and 44.3 % with at least one moderate-pDDI. Of 675 pDDIs, most were of moderate (63.6 %) or major severity (23 %); good (61.2 %) or fair (25.5 %) type of scientific evidence; and delayed onset (50.2 %). Most frequently identified major or moderate interactions resulted in 45.3 % of all pDDIs. Their potential adverse outcomes included hepatotoxicity, bleeding, ototoxicity, nephrotoxicity, hypoglycemia, hyperglycemia, risk of thrombosis, hypotension, cardiac arrhythmias and reduction in therapeutic-effectiveness. There was significant association of the occurrence of pDDIs with patients’ age of 60 years or more (OR = 2.1; 95 % CI = 1.3–3.3; p = 0.003), hospital stay of 6 days or longer (OR = 2.6; 95 % CI = 1.5–4.5; p = 0.001), and seven or more number of prescribed medications (OR = 5.9; 95 % CI = 3.6–9.6; p < 0.001). Conclusion The present study has recorded a high prevalence of pDDIs in internal medicine wards. Patients with old age, longer hospital stay and increased number of prescribed medications were at higher risk.