A study conducted by Wyeth et al evaluated the effects of single low doses of ranitidine on intragastric acidity.

Investigators assessed intragastric pH in 24 healthy male subjects for 9 h after lunch in five studies. Antacid was given to all participants on day 1. This was followed by single oral doses of a study drug 45 min post lunch on four different occasions. The participants received placebo and either ranitidine 25 mg, 75 mg or 125 mg.

• During the two post-dosing time periods (0-5 h and 5-9 h), significant reduction in integrated intragastric acidity was evident for all ranitidine doses in comparison with placebo (P < 0.0001).
• There was a greater reduction in acidity with increase in ranitidine dose (P < 0.0001).
• Time with pH > 3 was significantly longer for ranitidine 75 mg and 125 mg (P < 0.001), in comparison with placebo.
• The effect of the antacid was similar to placebo.

It was thus concluded that low doses of ranitidine led to a dose-related reduction in intragastric acidity for 9 h after administration.

Source: Wyeth JW, Pounder RE, Sercombe JC, Snell CC. The effects of low doses of ranitidine on intragastric acidity in healthy men. Aliment Pharmacol Ther. 1998 Mar;12(3):255-61.