Coppens et al conducted a study and measured intragastric acidity in 6 healthy volunteers and 8 patients with duodenal ulcer with the help of ambulatory 24 hour pH monitoring.

Each patient was randomized to receive placebo, 300 mg ranitidine at 19:00 h or 300 mg ranitidine at 22:00 h, on three different occasions. Validation of the method was attained by comparing the values indicated by the intragastric electrode and the pH of simultaneously aspirated gastric juice.

On comparing the area under the curve of intragastric hydrogen ion activity, and the percent of time below pH 5, investigators noted that ranitidine administered at 19:00 h led to better inhibition of nocturnal acidity (20.00 h-08.00 h) compared to the drug administered at 22:00 h (p less than 0.01).

There appeared to be no significant difference in daytime acidity between both ranitidine regimens and placebo.

Timing of administration of ranitidine thus seems to have an impact on inhibition of gastric acidity.

Source: Coppens JP, Warzee P, Schapira M, et al. Single dose ranitidine: influence of the time of administration on gastric acidity in normal subjects and in patients with duodenal ulcer. Gastroenterol Clin Biol. Jun-Jul 1988;12(6-7):537-41.