Histamine H2 receptor antagonists for decreasing gastrointestinal harms in adults using acetylsalicylic acid: systematic review and meta-analysis

BACKGROUND It is unclear if histamine H2 receptor antagonists (H2 blockers) prevent a variety of gastrointestinal harms among patients taking acetylsalicylic acid (ASA) over long periods. METHODS Electronic databases (e.g., MEDLINE, Embase and Cochrane Central Register of Controlled Trials; from inception to November 2010) and reference lists of retrieved articles were searched. Randomized placebo-controlled trials (RCTs) assessing the efficacy of H2 blockers in reducing gastrointestinal harms (bleeding, ulcers) among adults taking ASA for 2 weeks or longer were included. Two reviewers independently abstracted study and patient characteristics and appraised study quality using the Cochrane risk-of-bias tool. Peto odds ratio (OR) meta-analysis was performed, 95% confidence intervals (CIs) were calculated, and statistical heterogeneity was assessed using the I (2) and χ(2) statistics. RESULTS Six RCTs (4 major publications and 2 companion reports) with a total of 498 participants (healthy volunteers or patients with arthritis, cardiovascular or cerebrovascular disease, or diabetes mellitus) were included. One trial adequately reported allocation concealment and sequence generation, with the other 3 trials being judged as unclear for both aspects. In one RCT, no statistically significant differences for gastrointestinal hemorrhage requiring admission to hospital (p = 0.14) or blood transfusion (p = 0.29) were observed between the group receiving concomitant famotidine and ASA and the group receiving concomitant placebo and ASA. After a median of 8 weeks' follow-up, H2 blockers were more effective than placebo in reducing gastrointestinal hemorrhage (2 RCTs, total of 447 patients, OR 0.07, 95% CI 0.02-0.23) and peptic ulcers (3 RCTs, total of 465 patients, OR 0.21, 95% CI 0.12-0.36) among patients taking ASA for 2 weeks or longer. Despite substantial clinical heterogeneity across the studies, including types of H2 blockers, dosing of ASA and underlying conditions, no statistical heterogeneity was observed. INTERPRETATION H2 blockers reduced gastrointestinal harm among patients taking ASA for 2 weeks or longer. These results should be interpreted with caution, because of the small number of studies identified for inclusion.