Famotidine increases plasma alcohol concentration in healthy subjects

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.

Pharmacokinetic interactions between alcohol and other drugs

The frequent use of alcohol (ethanol) together with prescription drugs gives any described pharmacokinetic interaction significant clinical implications. The issue is both the effect of alcohol on the pharmacokinetics of various drugs and also the effect of those drugs on the pharmacokinetics of alcohol. This review discusses these pharmacokinetic interactions but also briefly describes some other effects of alcohol that are clinically relevant to drug prescribing. The use of several different study designs may be required before we can confidently state the presence or absence of any alcohol-drug interaction. Short term administration of alcohol in volunteers is the most common study design but studies of social drinking and prolonged moderate alcohol intake can be important in some situations. Community-based studies may illustrate the clinical relevance of any interaction. Alcohol can affect the pharmacokinetics of drugs by altering gastric emptying or liver metabolism (by inducing cytochrome P450 2E1). Drugs may affect the pharmacokinetics of alcohol by altering gastric emptying and inhibiting gastric alcohol dehydrogenase. The role of gastric alcohol dehydrogenase in the first-pass metabolism of alcohol is reviewed in this article and the arguments for and against any potential interaction between alcohol and H2 receptor antagonists are also discussed. The inhibition of the metabolism of acetaldehyde may cause disulfiram-like reactions. Pharmacodynamic interactions between alcohol and prescription drugs are common, particularly the additive sedative effects with benzodiazepines and also with some of the antihistamine drugs; other interactions may occur with tricyclic antidepressants. Alcohol intake may be a contributing factor to the disease state which is being treated and may complicate treatment because of various pathophysiological effects (e.g. impairment of gluconeogenesis and the risk of hypoglycaemia with oral hypoglycaemic agents). The combination of nonsteroidal anti-inflammatory drugs and alcohol intake increases the risk of gastrointestinal haemorrhage.

Cimetidine inhibition of human gastric and liver alcohol dehydrogenase isoenzymes: identification of inhibitor complexes by kinetics and molecular modeling

Cimetidine, an H2-receptor antagonist, is one of the most commonly prescribed drugs in the world. It has been reported to increase blood alcohol concentrations in drinking individuals. To determine if this increase could be due to inhibition of alcohol dehydrogenase activity, the effect of the drug on ethanol oxidation by gastric sigma sigma alcohol dehydrogenase and liver beta 2 beta 2, pi pi, and chi chi alcohol dehydrogenase isoenzymes was observed. Cimetidine inhibited all isoenzymes studied except chi chi; the chi chi isoenzyme showed no inhibition up to 5 mM cimetidine. Inhibition of the alcohol dehydrogenase isoenzymes by the H2-receptor antagonists nizatidine, ranitidine, and famotidine was negligible. Docking simulations with the beta 2.NAD+.4-iodopyrazole X-ray structure indicated that cimetidine fit well into the substrate binding site. The substitution on the thiazole ring of nizatidine, however, prevented docking into the binding site. Cimetidine inhibition of ethanol oxidation by sigma sigma and beta 2 beta 2 was competitive with varied ethanol, exhibiting Ki values of 2.8 +/- 0.4 mM and 0.77 +/- 0.07 mM, respectively. Cimetidine inhibition of ethanol oxidation by pi pi was noncompetitive with varied ethanol (Ki = 0.50 +/- 0.03 mM). Inhibition of ethanol oxidation by sigma sigma and beta 2 beta 2 with varied NAD+ was competitive. These results, together with the cimetidine inhibition kinetics of acetaldehyde reduction by sigma sigma and beta 2 beta 2, with either varied NADH or varied acetaldehyde, are consistent with cimetidine binding to two enzyme species. These species are free enzyme and the productive enzyme.NAD+ complex.