Drug-drug interactions among recently hospitalised patients--frequent but mostly clinically insignificant.

OBJECTIVE: Patients use and store considerable amounts of drugs. The aim of the present study was to identify potential drug-drug interactions between drugs used by patients recently discharged from the hospital and, subsequently, to estimate the clinical implications of these interactions.
METHODS: Patients were visited within 1 week following their discharge from hospital and interviewed about their drug use. Stored products were inspected. We used a bibliography (Hansten and Horn; Wolters Kluwer Health, St. Louis, Mo., 2004) to identify and classify potential drug-drug interactions.
RESULTS: In total, 83 surgical and 117 medical patients (n = 200) were included in the survey, of which 139 (70%) were women. The median age was 75 years (range: 24-100 years). Patients stored 2119 medications at home (median: nine per patient; range: 2-44) and used 1622 medications daily or on demand (median: eight per patient; range: 1-24). With respect to those drugs used daily or on demand, 476 potential interactions were identified (126 patients); none were class 1 (always avoid drug combination) and 25 were class 2 (usually avoid combination; 24 patients). Eleven of the potential class 2 interactions involved over-the-counter products (aspirin and ginkgo biloba). Of the 52 drugs involved in potential class 2 interactions, 50 had been used for more than 1 month. According to the hospital case notes, none of the potential class 2 interactions had actually caused adverse effects.
CONCLUSION: Although potential drug-drug interactions are highly prevalent, serious and clinically significant interactions are rare among recently hospitalised patients.