Purpose: Adverse drug reactions due to drug-drug interactions (DDIs) are important in drug safety. The aim of this study was to check potential DDIs (pDDIs) on hospital admission and discharge and to evaluate admissions due to DDIs in medical departments of a primary city and tertiary referral hospital.
Methods: Age, sex, presence of renal and liver failure, drug information, diagnosis, and urgency and reason for admission were retrospectively recorded in 520 randomly selected patients in medical departments of the University Medical Center Ljubljana. The screening program Drug-Reax was used to check for pDDIs in patients with drug information on both admission and discharge home, and the proportion of patients admitted as the consequence of a DDI was estimated.
Results: Overall, 14.6% (76/520) of patients had incomplete information on drug names in their medical documentation on admission; at the end of treatment 12.5% (52/416) of patients were discharged home with incomplete information on drug names in their discharge letters. A total of 323 patients had complete information on drug names on both admission and discharge and were included in the analysis of pDDIs: 51% (166/323) of patients on admission and 63% (204/323) on discharge had at least one pDDI (P = 0.001). Major pDDIs were found in 13% (41/323) of patients on admission and 18% (59/323) on discharge (P = 0.001). An ACE inhibitor combined with spironolactone was the most common major pDDI, representing 20.0% of all pDDIs on admission and 25.6% on discharge. Among patients with pDDI on admission, 2.4% (4/166) of were admitted because of an ADR caused by a DDI. Overall, 1.2% (4/323) of patients were admitted as the consequence of a DDI.
Conclusions: The information on patient medication on hospital admission and discharge is incomplete. Half of patients on admission and almost two-thirds on discharge had pDDIs. ADRs due to DDIs caused 1.2% of admissions to medical departments in Ljubljana's primary city and tertiary referral hospital.