When It Is Safe To Drink Alcohol After Metronidazole?

Jammie asked

I took Flagyl at 7:30 yesterday morning. I'm going to a wedding, am I able to drink?

Answer

While taking metronidazole (Flagyl), consumption of alcohol is contraindicated until at least three days after taking the last dose.

The interaction between alcohol and metronidazole can cause serious abdominal cramps, nausea, vomiting, headaches, and flushing.

In addition, alcohol can decrease immune function and worsen side effects of antibiotics like nausea, diarrhea, and upset stomach. While recovering from an infection, it is important to stay well hydrated and get plenty of rest.

Metronidazole has a half-life of about 8 hours. This means that it takes about 8 hours for the drug concentration to reach 50% of its maximum concentration. After 5-6 half-lives (~45 hours), metronidazole will be out of the system. Because each person metabolizes drugs at a different pace, waiting 72 hours would ensure metronidazole is out of the system.

How Alcohol Is Metabolized

Alcohol is primarily metabolized via alcohol dehydrogenase, aldehyde dehydrogenase, cytochrome P450 (CYP2E1), and catalase.

The byproducts of alcohol include acetaldehyde and acetate and contribute to many of the negative effects. Genetic variation of these enzymes causes varying degrees of alcohol metabolism—which is why everyone tolerates alcohol differently. This metabolism takes place mostly in the liver.

CYP enzymes play a particularly important role in drug metabolism and drug interactions occur via the inhibition or induction of these enzymes. Alcohol does impact CYP enzymes, especially CYP2E1.

Disulfiram-Like Reaction

Some drugs may cause a “disulfiram-like reaction” when taken with alcohol. This can cause flushing, nausea, vomiting, and general “hangover effects”. These drugs inhibit aldehyde dehydrogenase which is crucial in the metabolism of alcohol. Some of these drugs are thought to include metronidazole, disulfiram, and chloramphenicol.

Disulfiram is actually used clinically to treat alcohol dependence since it makes drinking alcohol much less desirable.

Although the package insert strongly recommends against using alcohol with metronidazole, the published evidence is unclear.

There have been case studies pointing to the interaction causing severe side effects and even death.

However, other small studies did not show that metronidazole increased acetaldehyde levels in the blood or cause any noticeable adverse events. Unfortunately, there are no large studies analyzing this interaction and it is possible that some groups of people would have significant adverse reactions.

Although the evidence of metronidazole causing a disulfiram-like reaction is limited, the drug manufacturer states that alcohol should NOT be consumed within three days of taking metronidazole. Because the risk of taking these together is significant, it would be smart to wait to drink until the risk of a disulfiram-like reaction is decreased.