Savarino et al conducted a study to determine the effects of placebo twice a day (bid), nizatidine 150 mg bid, nizatidine 300 mg bid, and ranitidine 300 mg bid on gastric acidity using continuous 24-hour intra gastric pH monitoring.

The study recruited 12 patients with duodenal ulcer in remission. The patients were randomly allocated to receive the medications on four different occasions in a single-blind fashion, at a gap of at least 1 week.

• The active treatment regimens led to higher pH values (P < 0.001) and gastric pH was maintained at >3.0 for a longer period of time (P <0.001), compared to placebo at all time intervals except evening.
• Nizatidine 150 mg bid was associated with a lower increase in pH compared to nizatidine 300 mg bid (P < 0.01) and ranitidine 300 mg bid (P < 0.05) during the daytime as well as the entire 24-hour period.
• Nizatidine 150 mg bid maintained gastric pH at or > 3.0 units for a shorter duration compared to its 300 mg bid regimen (P <0.01) and ranitidine 300 mg bid (P < 0.05) during the 24-hour period and during daytime.
• Twice daily doses of H2 blockers appear to be more effective than placebo in reducing gastric acidity.
• A 300 mg bid regimen of both nizatidine and ranitidine yields significantly greater acid suppression which also lasts longer, compared to 150 mg bid nizatidine.

Source: Savarino V, Mela GS, Zentilin P, et al. Twenty-four-Hour Control of Gastric Acidity by Twice-Daily Doses of Placebo, Nizatidine 150 mg, Nizatidine 300 mg, and Ranitidine 300 mg. J Clin Pharmacol 1993;33:70-74.