The prevalence of potential drug-drug interactions in patients with heart failure at hospital discharge.

Background/objective: Pharmacotherapy for heart failure is complex and, due to polypharmacy, is associated with a large risk of potential drug-drug interactions (DDIs). The objective of the present study was to assess the prevalence of potential DDIs in the medication of hospitalised heart failure patients and to evaluate their clinical relevance.

Study Design/methods: The medication of 400 patients was retrospectively analysed for potential DDIs at hospital admission and discharge using a computerised drug interaction program. Main inclusion criteria were the diagnosis of heart failure and a minimum of two drug prescriptions at discharge.

Results: In the study population of 400 heart failure patients (median age 79 years, 55.5% men), the median number of drugs per patient was lower at admission than at discharge (6 [interquartile range {IQR} 4-9] vs 8 [IQR 6-10]; p < 0.001). At hospital admission, a total of 863 potential DDIs were detected in 272 patients (68.0%; 95% CI 63.4, 72.6). At discharge, 1171 potential DDIs were detected in 355 patients (88.8%; 95% CI 85.7, 91.8). This corresponds with a significant increase in the median number of potential DDIs per patient from admission to discharge (1.5 [IQR 0-3] vs 3 [IQR 1-4]; p < 0.001). Of the 1171 potential DDIs at discharge, 432 (36.9%) were prevalent at admission and 739 (63.1%) resulted from a medication change during the hospital stay. Of these 739 new potential DDIs, the severity of the potential adverse effect was rated as 'major' in 190 (25.7%) patients, 'moderate' in 482 (65.2%) and 'minor' in 67 (9.1%). The 190 potential DDIs with major severity were recorded in a total of 145 patients (36.3%; 95% CI 31.5, 41.0%). Hyperkalaemia was the most prevalent potential adverse effect of major severity (n = 93) and the combination of an ACE inhibitor with a potassium-sparing diuretic was recorded in 64 (16.0%) patients.

Conclusions: The study shows that hospitalisation of patients with heart failure results in an increase in the number of drugs prescribed per patient and, thereby, also in the number of potentially interacting drug combinations per patient. Although electronic drug interaction programs are a valuable tool to check for potential DDIs, the clinical relevance of most potential DDIs can only be judged by assessment of the individual patient.