Effect of cimetidine on the pharmacokinetics of theophylline.

1. The effect of the therapeutic doses of cimetidine (400 mg/twice daily) on theophylline metabolism in Jordanian volunteers was studied. 2. The administration of the above therapeutic cimetidine dose did not alter theophylline clearance and elimination half-life. 3. Cimetidine administration also failed to alter the elimination of theophylline metabolites in urine.