PROCAINAMIDE-CIMETIDINE DRUG-INTERACTION IN ELDERLY MALE-PATIENTS

Thirty‐six hospitalized male patients receiving oral sustained‐release procainamide every six hours for the treatment of ventricular arrhythmias were studied at steady‐state before and after oral cimetidine 300 mg every six hours for three days. Average age and weight were 73 ± 12 (SD) years and 76 ± 10 kg. Patients did not have a myocardial infarction within the last two years or congestive heart failure and had calculated creatinine clearances (CrCl) between 35 and 75 mL/min/70 kg. Ten patients had urine collections that permitted computation of the ratio between the renal clearance of procainamide and CrCl (PA/CrCl) and the renal clearance of n‐acetylprocainamide (NAPA) and CrCl (NAPA/CrCl). The average steady‐state procainamide and NAPA concentrations increased 55% and 36%, respectively, during cimetidine treatment (P < .01). Twelve patients experienced mild to severe symptoms of what may have been procainamide toxicity. Apparent procainamide oral clearance decreased 41% while patients received cimetidine (P < .01). PA/CrCl and NAPA/CrCl ratios decreased by 33% and 21%, respectively, during cimetidine therapy (P < .05). Cimetidine therapy given to older male patients taking procainamide can cause steady‐state concentrations of procainamide to rise to toxic levels. Patients prescribed this combination should be monitored carefully for adverse side effects. 1990 The American Geriatrics Society