Metronidazole
antibiotic
Third-party optionBy the Layer Nutrition editorial team · How the atlas classifies the 664 molecules
What this medicine is for
Pharmacologically, Metronidazole relates to the category “antibiotic”. Antibiotics treat infections caused by bacteria. They are taken as a course, over a set duration, until the end of the prescription.
In practical terms, for Metronidazole: Treats certain bacterial and parasitic infections. It is used rather on an occasional basis or as a short course, for the time needed to get through an episode.
Under which brands it is found
In France, about 23 reimbursable presentations containing Metronidazole are recorded. It comes under various trade names and in generic form.
- Birodogyl
- Flagyl
- Metronidazole Arrow
- Metronidazole B Braun
- Metronidazole Baxter
- Metronidazole Biogaran
- Metronidazole Noridem
- Pylera
- and other presentations
Generics and the original brand are equivalent for the active substance; only the appearance, the name or the excipients may differ.
At the table: eating despite the metallic taste
Metronidazole often leaves a metallic taste in the mouth and can cause nausea, two frequent effects that interfere with meals. Taking the tablet during a meal limits stomach discomfort, and food helps you keep eating normally during the course.
When you feel queasy, mild and easily digested foods go down better: whole rice, white fish, potato, banana. Plain yogurt provides ferments and slips easily into a meal, alongside your treatment. Eating at the same time as the dose softens the passage of the medicine through the stomach.
Faced with the metallic taste, many people tolerate fresh, tangy foods better, such as oranges and red berries, which wake up the palate. Throughout the treatment and for at least three days after the last dose, alcohol remains to be avoided, including when hidden in certain sauces and desserts, because it triggers an unpleasant reaction with flushing and nausea.
How metronidazole works
Metronidazole enters the microbial cell by simple diffusion, without a dedicated transporter. Once inside, its nitro group is reduced by an enzyme specific to anaerobic microorganisms and protozoa, pyruvate-ferredoxin oxidoreductase. This reduction generates highly reactive free radicals that break the strands of DNA and cause it to lose its helical structure. Deprived of intact DNA, the germ can no longer replicate and dies.
This activation only takes place in an environment with a low oxidation-reduction potential, that of anaerobic metabolism. Metronidazole therefore strikes anaerobic bacteria and protozoa, but has no effect on aerobic bacteria, which do not reduce its nitro group. Its mean elimination half-life is eight hours in a healthy subject, which sets the rhythm of the doses across the day.
Why it is prescribed
Metronidazole covers several protozoal infections: trichomoniasis, amebiasis and giardiasis. It also treats bacterial vaginosis and infections caused by anaerobic bacteria, in particular intra-abdominal infections. Its range of action overlaps exactly with the germs that thrive in the absence of oxygen, where its mechanism can be activated.
Outside its marketing authorization, it is also used against Clostridioides difficile, an anaerobic bacterium responsible for diarrhea after antibiotic therapy. The doctor chooses the molecule according to the targeted germ and its location. The length of the course is set by the indication, and the treatment is carried through to the end.
How to take it day to day
The oral dose can be taken during a meal to limit stomach discomfort. Eating at the same time does not reduce the total amount of medicine absorbed: the meal only lowers the concentration peak and delays the moment when this peak is reached. Overall efficacy remains the same, and digestive comfort improves.
With a half-life of eight hours, taking the doses regularly keeps an active concentration stable. Metronidazole is transformed by the liver, through oxidation of its side chain and glucuronidation, and 60 to 80 % of the dose leaves in the urine. The course must be carried through to the end and not stopped on one's own as soon as the signs ease off, at the risk of letting the infection return.
The effects to know about and their frequency
The most reported adverse effects are headaches, in about 18 % of people, and vaginitis, in 15 %. Next come nausea, from 10 to 12 %, and a characteristic metallic taste in 9 %. Genital itching affects around 5 %, dizziness and diarrhea each 4 %. The metallic taste and nausea are among the most frequent and can interfere with eating during treatment.
Rarer but serious neurological effects have been described: encephalopathy, peripheral neuropathy sometimes affecting the optic nerve, and seizures. The neurological risk increases with prolonged or repeated courses. When such signs appear, stopping the treatment may become necessary, and any new neurological symptom must be reported to the doctor without delay.
Alcohol and drug interactions
Alcohol is to be avoided throughout the treatment and for at least three days after the last dose, including products containing alcohol or propylene glycol. The combination triggers a disulfiram-like reaction, with flushing, tachycardia, nausea, vomiting and abdominal cramps. Concurrent use of disulfiram itself is not advised, since psychotic reactions have been reported in alcoholic patients taking both molecules together.
Metronidazole strengthens the effect of coumarin anticoagulants such as warfarin, with a lengthening of the prothrombin time and therefore an increased risk of bleeding. A short course has also been associated with a rise in lithium levels and, in a few cases, with signs of lithium toxicity. These two treatments call for particular vigilance when combined with metronidazole.
Monitoring during treatment
During prolonged or repeated courses, a complete blood count with white blood cell differential is recommended, because metronidazole can cause leukopenia and neutropenia. Neurological monitoring accompanies these long courses, in order to detect neuropathy or other signs of nervous system involvement early.
In people treated with warfarin, the prothrombin time, expressed by the INR, is checked throughout the combination. In those taking lithium, the lithium level is measured in the same way. These measurements adjust the doses and avert complications before they set in.
Sources
Related molecules
To explore in the « Anti-infectives » family and its neighbours.
See the whole « Anti-infectives » family · Back to the atlas
Supplements to consider
Beyond the plate, a single isolated nutrient can be worth discussing, to confirm with your doctor or pharmacist. Here is which one and in which form.
Probiotics
Probiotics are live micro-organisms, mainly lactobacilli and bifidobacteria. The CFU count and the number of strains are among the selection criteria; gastro-resistant capsules protect the bacteria from stomach acidity.
Preferred form gastro-resistant capsules, several strains, CFU count stated
Frequently asked questions
What is metronidazole (Flagyl) used for?
Metronidazole is an antibiotic prescribed for certain bacterial and parasitic infections, particularly digestive, gynecological, or dental ones. It is a prescription medication, and its precise indication depends on your situation: refer to the leaflet and to your doctor or pharmacist.
Can you drink alcohol while taking metronidazole?
The leaflet advises against alcohol during treatment and in the days following your last dose: the combination can trigger what is known as a disulfiram-like (antabuse) reaction (flushing, nausea, vomiting). For the exact length of time to observe, refer to the leaflet and to your pharmacist.
What are the side effects of metronidazole?
The leaflet notably mentions digestive disturbances, a metallic taste, dizziness and, more rarely, neurological or visual disturbances that can impair driving. Any unusual or persistent effect should be discussed with your doctor or pharmacist, drawing on the leaflet.
Does metronidazole interact with other medications?
Yes, the leaflet flags interactions, for example with certain anticoagulants such as warfarin or with lithium. Report all your treatments, including over-the-counter ones, to your doctor or pharmacist, and check the leaflet before combining anything.
Can metronidazole disrupt your gut flora?
Like antibiotics in general, metronidazole also acts on the bacteria in the digestive tract, and research links antibiotic use to a transient alteration of the microbiota and to what is known as antibiotic-associated diarrhea in some patients. These effects and their management should be discussed with your doctor or pharmacist.
Which probiotics to consider while taking metronidazole, and in what form?
Some studies associate taking probiotics with better digestive tolerance during antibiotic treatment, with results that vary depending on the strains. The most studied strains for antibiotic-associated diarrhea are the yeast Saccharomyces boulardii and certain Lactobacillus, generally in the form of capsules or sachets taken apart from the antibiotic dose. To be confirmed with your pharmacist based on your situation.
Ces réponses portent sur le volet nutritionnel. Pour toute question sur votre médicament, la notice et votre médecin ou pharmacien font foi.