Hamilton and colleagues conducted a study to evaluate the duration of action of single doses of ranitidine 75 mg, cimetidine 200 mg and placebo on intragastric acidity in healthy individuals.

The study included 30 healthy individuals with no history of peptic disease. Intragastric acidity was measured following a single oral dose of either of the three administered after lunch.

• The percentage reduction in intragastric acidity with the two drugs, in comparison with placebo, during daytime was 59% for ranitidine (P < 0.001) and 35% for cimetidine (P < 0.001).
• Ranitidine was better at inhibiting intragastric acidity compared to cimetidine (P < 0.001).
• With placebo, the mean daytime intragastric acidity (0-10 hr after dose) was 37.62 mmol/l, while it was 17.21 mmol/l with ranitidine and 25.06 mmol/l with cimetidine.
• Mean nighttime (10-20 hr after-dose) intragastric acidity with placebo was 34.37 mmol/l, 29.06 mmol/l with ranitidine and 33.85 mmol/l with cimetidine.
• Ranitidine decreased night-time intragastric acidity by 18% compared to placebo (P< 0.01); however, cimetidine appeared to have no significant effect during this period (2%, NS).
• Ranitidine inhibited acidity to a greater extent than cimetidine (P = 0.043).

It was concluded that ranitidine inhibits intragastric acidity for 0-15 hr following an oral dose, while cimetidine exerts little inhibitory effect after 10 hr.

Source: Hamilton MI, Sercombe J, Pounder RE. Decrease of intragastric acidity in healthy subjects dosed with ranitidine 75 mg, cimetidine 200 mg, or placebo. Dig Dis Sci. 2002 Jan;47(1):54-7.