THE CLINICAL RELEVANCE OF THE INTERACTION BETWEEN CARBAMAZEPINE AND DEXTROPROPOXYPHENE IN ELDERLY PATIENTS IN GOTHENBURG, SWEDEN

Objectives: To evaluate the clinical importance of the interaction bet ween carbamazepine (CBZ) and dextropropoxyphene in elderly patients. M ethods: All patients (n = 7263) in Gothenburg, Sweden, who were part o f a drug-dispensing programme, were included in the study. Eight per c ent of the patients took CBZ and 18% took dextropropoxyphene, continuo usly. Patients who used a combination of these drugs were compared wit h patients who took only CBZ or dextropropoxyphene or neither of the t wo drugs. These four groups of patients were matched to each other wit h reference to gender, age and concomitant medication, which finally r esulted in 21 patients in each group. A questionnaire with 30 symptoms of well-being, including symptoms typical of adverse effects of CBZ, were answered by the patients with the help of a registered nurse. Ven ous blood samples were drawn from the patients for the analysis of CBZ , its metabolite CBZ 10,11-epoxide (CBZ-E) and dextropropoxyphene. Res ults: The doses of CBZ and dextropropoxyphene were lower among patient s who used the combination of the two drugs than among those who only used one of the drugs. The mean level of CBZ in serum (S-CBZ) was, how ever, significantly higher and the level of CBZ-E in serum (S-CBZ-E) s ignificantly lower among the patients who used the combination of CBZ and dextropropoxyphene, thus indicating an inhibition of the metabolis m of CBZ. The prevalence of symptoms indicating side effects of CBZ wa s significantly higher in the group of patients who used both drugs. C onclusion: This study has shown that the combination of CBZ and dextro propoxyphene is hazardous in elderly patients and should be used with caution.