Interaction between carbamazepine and propoxyphene in man.

This investigation was carried out because of a clinical suspicion of drug interaction between Propoxyphene (PRX) hydrochloride and Carbamazepine (CBZ). Seven out-patients, six suffering from epilepsy and one from trigeminal neuralgia, treated with CBZ alone or in combination with phenobarbitone, received PRX hydrochloride capsules, 65 mg three times a day. Two patients stopped the PRX intake after 2 days due to severe side effects. Three of the remaining patients had symptoms and signs of drug intoxication. Blood samples were examined by thin-layer chromatography. A marked increase (45-77 per cent) in CBZ plasma level was found in all patients on combined treatment of CBZ and PRX. There were no significant changes in CBZ-10,11-epoxide level. The results suggest an inhibition of CBZ metabolism when CBZ and PRX are administered simultaneously.