A study was conducted on 30 healthy volunteers who were subjected to four separate 24-hour studies at least one week apart. In this double-blind study, continuous measurement of 24-hour intragastric acidity was done in these volunteers during treatment with placebo, cimetidine 800 mg, ranitidine 300 mg, or famotidine40 mg given after the evening meal (post cenam nocte, PCN).

Median 24-hour acidity was found to decrease with all the H₂-receptor antagonists from 25.1 mmol/l on placebo to 10 mmol/l (-60. 1%) with cimetidine, to 3.2 mmol/l (-87.25%) with ranitidine and to 2.5 mmol/l (-90.0%) with famotidine (p<0.0005). All the study drugs led to significant inhibition of night time acidity.

Famotidine and ranitidine were found to be more potent inhibitors of gastric acidity compared to cimetidine.

The findings suggested that famotidine and ranitidine led to significantly greater acid reduction in comparison with cimetidine, and no difference was observed between famotidine and ranitidine.

Source: Merki HS, Witzel L, Walt RP, et al. Double blind comparison of the effects of cimetidine, ranitidine, famotidine, and placebo on intragastric acidity in 30 normal volunteers. Gut 1988;29:81-84.