POTENTIAL DRUG-DRUG INTERACTIONS IN 5,125 MOSTLY ELDERLY OUT-PATIENTSIN GOTHENBURG, SWEDEN

Of 5,125 mostly elderly out-patients, average age 78.2 years, 1,594 (3 1%) had at least one interacting drug combination according to the Swe dish National Formulary. On average, each patient with drug-drug inter actions (DDIs) had 1.6 DDIs. There was no difference in the sex or age between those having DDIs and those without. However, patients with o ne or more DDIs used a significantly larger number of drugs than those without DDIs, on average 8.1 versus 5.2. This significant difference was independent of age and sex. When classified for clinical significa nce according to the handbook ''Drug Interactions and Updates'' by Han sten and Horn, 155 (3%) patients had interactions of 'major clinical s ignificance'. The most common were interactions between beta-adrenergi c blockers and antidiabetics, followed by potassium-sparing diuretics and potassium, and carbamazepine and dextropropoxyphene. The methodolo gy allows us to screen routinely for DDIs and to plan further studies with emphasis on clinical outcome.