Background
Despite the widespread use of over‐the‐counter H2‐receptor antagonists little is known about their duration of action on human gastric acid secretion. There are studies reporting inhibitory effects for up to 9 h post‐dose but few data beyond this period.
Methods
Profiles of 20‐h intragastric acidity were measured simultaneously in 24 healthy subjects who were dosed (at 12.30 h) with either ranitidine 75 mg, cimetidine 200 mg or placebo in a three‐way crossover study, according to a standard protocol. Five‐millilitre aliquots of gastric juice were aspirated half‐hourly during the day (0–10 h post‐dose) and hourly overnight (10–20 h post‐dose). pH was measured to three decimal places with a glass electrode. Weighted intragastric acidity (AUC/time) was calculated for both day‐ and night‐times using 2.5‐h intervals during the day and 5‐h intervals at night. Statistical analysis was by ANOVA.
Results
The results are expressed as mean weighted intragastric acidity (mmol/L). (i) Daytime (0–10 h post‐dose): when dosed with placebo the weighted intragastric acidity was 31.03, decreasing to 10.37 (P < 0.001 vs. placebo) and 16.23 (P < 0.001 vs. placebo) when treated with ranitidine and cimetidine, respectively. Ranitidine inhibited weighted intragastric acidity to a greater degree than cimetidine (P < 0.001) during this period. (ii) Night‐time (10–20 h post‐dose): when dosed with placebo the weighted intragastric acidity was 21.36 decreasing to 16.65 (P < 0.001 vs. placebo) when dosed with ranitidine and remaining unchanged at 20.03 (P = 0.886 vs. placebo) when dosed with cimetidine. Ranitidine inhibited weighted intragastric acidity to a greater degree than cimetidine (P = 0.010) during this period. A sub‐analysis of the two 5‐h intervals showed that compared to placebo, ranitidine inhibited weighted intragastric acidity significantly in the 10–15 h period. However, its effect in the 15–20 h period did not differ from placebo.
Conclusions
In healthy subjects, the inhibitory effect of ranitidine 75 mg on intragastric acidity can be detected 10–15 h after an oral dose. By contrast, the inhibitory effect of cimetidine 200 mg seems to be restricted to the first 10 h.