The effect of cimetidine on ethanol concentrations in fasting women and men after two different doses of alcohol

Is there an interaction between H2-antagonists and alcohol?

H2-antagonists are commonly prescribed drugs and alcohol use is widespread in the community. Any possible interaction may be important because of the frequent co-administration of both drugs and the potential for unexpected impairment of pyschomotor function, in particular, driving skills. Hepatic ADH is the major site of alcohol metabolism. ADH is also found in the stomach, but it is uncertain whether gastric ADH is able to metabolise a significant amount of alcohol in vivo. Significant first-pass metabolism can be demonstrated at lower doses of alcohol, and if alcohol is given after meals. Varying degrees of extraction of alcohol from the portal circulation probably explains the data regarding first pass metabolism rather than gastric metabolism by gastric ADH. H2-receptor antagonists inhibit gastric ADH activity to a variable extent. If gastric metabolism of alcohol is negligible then this inhibition has no relevance. Given the uncertainty regarding a mechanism of interaction, only carefully conducted studies in controlled environments will answer the question. The large inter-subject variability of alcohol absorption means that any study which seeks to determine the effect of an H2-receptor antagonist on ethanol metabolism must have sufficient numbers. A cross-over design, with each subject acting as his own control, is preferable to avoid ascribing an effect to treatment rather than to chance. The alcohol dosing studies are reviewed and the results summarised according to dose of alcohol given. At a dose of 0.15 g/kg of alcohol, four commonly used H2-antagonists may cause a small increase in blood alcohol concentrations in certain conditions. This absolute increase is very small. The magnitude of effect is far less than the effect of taking a meal before alcohol. At doses of 0.3 g/kg and above the majority of evidence favours no interaction between H2-antagonists and alcohol. There is no interaction at doses that would be expected to impair psychomotor skills (above 25 mg/dl). There remains a question regarding the cumulative effect of repeated small doses of alcohol and further studies are required. The relationship between ethanol absorption and gastric emptying raises the possibility that the effects of H2-receptor antagonists observed at very low doses of alcohol may be due to the acceleration of gastric emptying by these drugs. This is an attractive hypothesis that explains many aspects of the debate, but studies of the effect of H2-antagonists on gastric emptying have been conflicting.

Effect of histamine-2 receptor antagonists on blood alcohol levels: a meta-analysis

OBJECTIVE

To determine the effect, if any, of histamine type 2 receptor antagonists (H2RAs) on serum alcohol levels under various conditions including type of H2RA receptor antagonist, alcohol dose, and fed status of the subject.

STUDY DESIGN

Meta-analysis of the published literature.

DATA SOURCES

Studies were identified by MEDLINE (January 1982 through December 1997) using the key words H2 receptor antagonists and alcohol. Other studies were identified by reviewing bibliographies of retrieved articles and by discussion with colleagues.

STUDY SELECTION

Studies were selected if they involved the coadministration of H2RAs and alcohol in healthy, human volunteers. Studies that may have addressed this goal but were performed in another context, for instance the measurement of ulcer healing, were excluded.

DATA EXTRACTION

Data were extracted on the design, number of participants, participant characteristics, type and dose of H2RA administered, serum alcohol levels (measured as Cmax) along with standard deviations, dose of alcohol received, and fed or fasted status of participants. Alcohol dose was arbitrarily divided into low dose (< or = 0.5 g/kg body weight) versus high dose (> 0.5 g/kg body weight). In addition, studies involving ranitidine and cimetidine were stratified by sample size into small (n < or = 10) versus not small (n > 10).

MEASUREMENTS AND MAIN RESULTS

Twenty-four trials met selection criteria. Small elevations in Cmax were noted when cimetidine (2.71 mg/DL; 95% confidence internal [CI] 1.60, 3.83) or ranitidine (6.95 mg/DL; 95% CI 5.83, 8.08) were coadministered with alcohol. No such differences were noted for famotidine (0.28 mg/DL; 95% CI -1.24, 1.80) or nizatidine (2.33 mg/DL;, 95% CI -0.06, 4.72). The elevation detected with cimetidine and ranitidine was most pronounced in smaller studies (n < 10). Separate analyses investigating the effect of alcohol dose and fed or fasted status of participants revealed no clinically important differences.

CONCLUSIONS

Cimetidine and ranitidine, but not the other H2RAs, can cause small elevations of serum alcohol level when alcohol and drug are administered concurrently. Studies with larger numbers of participants were less likely to demonstrate this effect. Relative to accepted, legal definitions of intoxication, the effect of any H2RA on blood alcohol level is unlikely to be clinically relevant.