Comparison of the effects of placebo, ranitidine, famotidine and nizatidine on intragastric acidity by means of continuous pH recording.

The effects of single daily doses of placebo, nizatidine 300 mg, ranitidine 300 mg and famotidine 40 mg, given at 22.00 h, have been compared in 16 patients with healed duodenal ulcers. Each of them underwent the above treatment on four separate occasions. The three H2 receptor antagonists showed a significantly higher acid inhibition than placebo (p less than 0.003) throughout the whole 24-hour period. Famotidine turned out to be more effective than nizatidine (p less than 0.02) in reducing circadian acidity, while there was no difference between ranitidine and nizatidine. The effects of the three H2 blockers on overnight acidity (from 23.00 to 07.00) were similar to each other, whereas both famotidine (p less than 0.003) and ranitidine (p less than 0.02) produced more anacidity than nizatidine during the morning hours (from 07.00 to 12.00). The time period elapsed in consecutive minutes above 5.0 pH units during drug-related events was significantly longer with both famotidine (p less than 0.01) and ranitidine (p less than 0.01) compared to nizatidine. Therefore in the recommended dosages for clinical use the acid suppression of nizatidine was significantly shorter-lasting than that of both ranitidine and famotidine. The major change is represented by the lack of carryover effect of nizatidine on morning acidity.