Negative chronotropic effects of nizatidine.

Twelve healthy volunteers were given one week's oral treatment with each of 300 mg nizatidine, 40 mg famotidine, and placebo once daily in a randomised, placebo controlled, double blind study. Three hours after administration, nizatidine led to a significant reduction in the mean (SD) resting heart rate compared with placebo (63.6 (6.4) beats/minute on placebo to 55.9 (7.2) beats/minute on nizatidine (p less than 0.05)), whereas famotidine did not influence the heart rate significantly. Both drugs, however, increased significantly the pre-ejection period and the ratio of pre-ejection period to left ventricular ejection time on mechanocardiography and led to a significant decrease in cardiac output on impedance cardiography. The exercise heart rate on nizatidine as well as the resting heart rate on concurrent administration of nizatidine and the beta receptor blocking agent atenolol were subsequently investigated in the same volunteers. Nizatidine slightly inhibited exercise tachycardia by 4.4% (p less than 0.05). When compared with placebo, the mean resting heart rate was decreased on atenolol alone by a mean of 10.6 beats/minute (p less than 0.01) and fell further on co-administration with nizatidine to a total of 16.1 beats/minute (p less than 0.05 versus atenolol alone). In conclusion, the effect of nizatidine in reducing the heart rate needs careful evaluation in elderly patients with heart failure or those also taking beta blockers. In contrast to famotidine, long term treatment with 300 mg nizatidine a day has mainly negative chronotropic effects.