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-acetyl-procainamide (NAPA) and CrCl (NAPA/CrCl). The average steady-state procainamide and NAPA concentrations increased 55% and 36%, respectively, during cimetidine treatment (P less than .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 less than .01). PA/CrCl and NAPA/CrCl ratios decreased by 33% and 21%, respectively, during cimetidine therapy (P less than .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.
Bauer
L A
LA
Department of Pharmacy Practice, SC-69, University of Washington, Seattle 98195.
Black
D
D
Gensler
A
A
D000368:Aged; D000369:Aged, 80 and over; D001145:Arrhythmias, Cardiac / Q000188:drug therapy; D002927:Cimetidine / Q000009:adverse effects*; D004347:Drug Interactions; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic; D011342:Procainamide / Q000493:pharmacokinetics* / Q000506:poisoning
D002927:Cimetidine; D011342:Procainamide