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THE ACIDITY INDEX: A NOVEL MEASURE OF ACID SUPPRESSION TO COMPARE ORAL RABEPRAZOLE (RAB) AND INTRAVENOUS PANTOPRAZOLE (PAN) IN HEALTHY SUBJECTS

D Armstrong¹, C James¹, F Camacho², GLA Horbay³, B Teixeira³, FA Husein-Bhabha³
¹Division of Gastroenterology, McMaster University and Hamilton Health Sciences, Hamilton; ²Statistics, Damos Inc; ³Clinical Affairs, Janssen-Ortho Inc, Toronto, Ontario

The gastric acidity index (AI), reflects the luminal acid load, calculated as a function of hydrogen ion activity [H⁺] in the stomach, providing greater weighting to those periods during which pH is lower and the [H⁺] is logarithmically greater. It is thought to provide a more accurate assessment of the intragastric 'acid load' than % time pH>4 since it better quantifies the increasing potential for harm, the further gastric pH falls below 4. Recently, AI has been reported to provide a more complete description of the degree of acid suppression than more traditional measures of gastric acidity. The present, exploratory analysis compares the antisecretory effects produced by standard doses of oral RAB vs IV PAN in healthy volunteers.
METHODS: Double-blind, randomized, two-way crossover study in 38 Helicobacter pylori-negative healthy volunteers. Subjects received oral RAB 20 mg or IV PAN 40 mg once daily for 3 days, with a 14-day washout period before the second 3-day drug administration period with the crossover drug regimen. Intragastric pH was recorded continuously for 24-hours after a 7 am dosing on days 1 and 3 of each treatment phase. AI was calculated for the full 24-hours and for each 2-hour interval post-dosing on day 1 and 3.
RESULTS: Over a 24-hour period, mean AI (95% CI) was lower with oral RAB than IV PAN on day 1 [3625 (2963-4287) vs 5597 (4865-6329)] and day 3 [2154 (1723-2585) vs 3657 (3092-4222)]. AI was significantly lower with IV PAN only during the first 2 hours post-dose on days 1 and 3. During the next 2-hour period (2 to 4 hours post dose), AIs were not different between treatments on either day. For most of the remaining 2-hour intervals (between 4 and 24 hours post-dose on days 1 and 3), AI was significantly lower with oral RAB.
CONCLUSION: This exploratory analysis confirms that the AI can identify the greater acid suppression produced by oral RAB compared with IV PAN on days 1 and 3 of drug administration in healthy subjects. Further clinical studies are needed, in patients with esophagitis, to validate the clinical usefulness of AI in optimizing treatment choice.
Research funded by an unrestricted grant from Janssen-Ortho Inc, Toronto, Ontario

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