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.