Background: H2‐receptor antagonists are becoming widely available as over‐the‐counter medications for the treatment of heartburn and excess gastric acidity. Aim: To determine the effects of single low doses of ranitidine on intragastric acidity. Methods: Intragastric pH was measured for 9 h after lunch in five studies involving 24 healthy male volunteers. Antacid was given to all subjects on day 1. They then received single oral doses of a study drug 45 min after lunch on four separate occasions: placebo and either ranitidine 25 mg, 75 mg or 125 mg were given double‐blind according to a predetermined randomization schedule. Results: During both of the post‐dosing time periods (0–5 h and 5–9 h) there were significant decreases in integrated intragastric acidity for each ranitidine dose compared with placebo (P < 0.0001). There was a significant linear relationship between dose and integrated intragastric acidity with a greater decrease in acidity with increasing ranitidine doses (P < 0.0001). Compared with placebo, time with pH > 3 was significantly greater for ranitidine 75 mg and 125 mg (P < 0.001), but not ranitidine 25 mg. Results with the antacid were similar to placebo. Conclusions: Using low doses of ranitidine (25, 75 or 125 mg) there was a dose‐related decrease in intragastric acidity for 9 h after dosing. A single dose of antacid did not decrease intragastric acidity significantly.

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.

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Concomitant use of H 2 receptor antagonists and alginic acid compounds is common in the UK, although there is currently little supportive clinical data for this practice. This randomised, parallel group multi-centre study in general practice evaluates the efficacy of a new combination tablet containing cimetidine 200 mg and alginic acid 500 mg (Algitecv) in the treatment of symptomatic oesophageal reflux disease.Two hundred and eighty-six patients with reflux symptoms were randomly allocated to receive either the new tablet (2 tabs four times daily) or an alginic acid/antacid preparation (2 tabs four times daily) for six weeks. Data from 263 patients (132 cimetidine/alginic acid and 131 alginic acid/antacid) were available for the statistical analysis. A significantly greater reduction in the incidence and severity of heartburn was recorded in the cimetidine/alginic acid group compared with alginic acid/antacid. At Week 6, 61 per cent of patients in the cimetidine/alginic acid group reported complete relief of heartburn compared with 37 per cent in the alginic acid/antacid group (P=O.OOI). It is concluded that the cimetidine/ alginic acid combination tablet at 2 tabs four times daily is a more effective treatment for symptomatic oesophageal reflux disease than the widely prescribed alginic acid/antacid preparation used in this trial, also dosed at 2 tabs four times daily.

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