A 24-h intragastric acidity study is among the most useful tools to determine the effects of drugs on gastric acid secretion.

A study was conducted by Primrose et al to evaluate the effects of ranitidine at a dose of 300 mg b.d. and 300 mg q.d.s. compared to conventional dosing of 300 mg nocte, on 24-h intragastric pH and intragastric acidity among healthy volunteers.

This study was double-blind and included eight healthy male subjects with a mean (range) age of 19 (18-23) years. The participants were divided into groups being treated with 300 mg ranitidine nocte, 300 mg ranitidine b.d., 300 mg ranitidine q.d.s. and placebo for 2 days and were evaluated on the second day.

Findings of the study:

• When treated with placebo, the median 24-h pH was 1.45 (range 1.2-2.6), it was 2.6 (1.8-3.8) with 300 mg ranitidine nocte, 3.1 (2.2-6.0) with 300 mg ranitidine b.d. and 4.0 (2.2-5.0) with 300 mg ranitidine q.d.s. Additionally, 300 mg ranitidine nocte affected the daytime pH to a very less extent and night-time pH was least affected by 300 mg ranitidine q.d.s.
• The effects of both 300 mg ranitidine b.d. and 300 mg q.d.s. were significantly greater than 300 mg ranitidine nocte.
• All the treatment regimens significantly reduced the 24-h acidity (PË‚01).
• Treatment with 300mg ranitidine b.d. reduced the 24-h acidity to a greater extent than 300mg nocte (PË‚05).
• The percentage decrease in 24-h acidity was 61%, 77.7%, and 78% using 300 mg ranitidine nocte, 300mg b.d and 300mg q.d.s., respectively.
• Decrease in the daytime acidity was 42%, 77.8% and 88.9% when treated with the 300 mg ranitidine nocte, 300mg b.d and 300mg q.d.s., respectively.
• Further, the nocturnal acidity reduced by 92.9%, 90.0% and 65.5 %, respectively.
• Compared to placebo, 300mg ranitidine nocte and 300mg ranitidine b.d reduced the nocturnal acidity significantly.
• An almost near-maximal acid suppression was achieved at a dose of 600 mg/day.

Source: Primrose JN, Rogers MJ, Holmfield JHM. The effects of 300 mg ranitidine at night, twice daily and four times daily on intragastric acidity in normal subjects. Aliment Pharmacol Ther 1993; 7: 287-291.