Bauerfeind et al conducted a study to evaluate the antisecretory effect of ranitidine and famotidine given once a day. The drugs were administered either immediately following dinner or 3 hours after the meal.

This placebo-controlled multiple cross-over trial included 7 healthy individuals. The participants received either placebo, ranitidine 300 mg or famotidine 40 mg on six separate days at a gap of at least one week.

Investigators assessed 24-hour intragastric acidity. Duration of secretory inhibition was characterized as the period at night from the first rise in pH above till the final decline below 3.5.

• Secretory inhibition with early administration of ranitidine persisted for 10.7 hours while that with late administration lasted for 7.3 hours (p = 0.012).
• Secretory inhibition with early administration of famotidine continued for 10.1 hours and with late administration, it lasted for 7.1 hours (p = 0.005).
• Gastric acidity following dinner was found to be reduced by early but not by late administration of the drugs.

The efficacy of both ranitidine and famotidine was better when administered early, immediately after dinner.

Source: Bauerfeind P, Cilluffo T, Emde C, et al. Reduction of Gastric Acidity with Ranitidine or Famotidine: Early Evening Dosage Is More Effective than Late Evening Dosage. Digestion 1987;37:217–222.