Metronidazole

Generic name

Metronidazole

Active ingredient

Metronidazole

Product type

Small-molecule medicine

Drug class

Nitroimidazoles

Brand names

UK Flagyl, Rozex, Zidoval · US Flagyl, MetroGel

Routes

Oral, Topical, Vaginal, Rectal, Intravenous

Dosage forms

Tablet, Solution, Suppository, Gel, Cream, Injection

Usual preparations

Available as tablets, liquid, suppositories, skin gel and cream, vaginal gel, and as an injection given in hospital. (summary of the cited reference, not a prescription)

Onset and duration

The NHS says most infections start to improve within a few days, although the full course is still finished.

Monitoring

The NHS notes that metronidazole can affect the results of some blood tests, so it is mentioned before tests are arranged, and numbness or tingling in the hands and feet with longer use is a reason to speak to the prescriber.

Availability by country

Legal status differs between countries and can change; each row cites the document it was taken from and applies only to the country named.

What it is used for

• Bacterial skin infections and rosacea
• Mouth infections, including infected gums and dental abscesses
• Bacterial vaginosis and pelvic inflammatory disease
• Infected insect bites, skin ulcers, bed sores and wounds
• Trichomoniasis, a sexually transmitted infection, which the NHS says is usually treated with metronidazole

How it works in the body

Metronidazole is an antibiotic that treats bacterial and parasitic infections. Laboratory studies describe it as being switched on inside susceptible organisms, many of which live without oxygen, by pathways that human cells do not have. Once switched on, it forms short-lived chemical products that bind to DNA and damage it.

Cautions and interactions

• The NHS says to discuss metronidazole first if there has ever been an allergic reaction to it or another medicine, or if blood tests are planned, because it can interfere with some of them
• The NHS advises not drinking alcohol while taking metronidazole tablets or liquid or using suppositories, and avoiding it for 2 days after finishing, as the combination can cause feeling or being sick, stomach pain, hot flushes, palpitations and headache; the NHS trichomoniasis page gives at least 24 hours and MedlinePlus at least 3 days, so advice differs between pages
• The NHS also lists feeling unable to stop drinking alcohol during treatment as a reason to talk to the prescriber first
• Liver problems, dialysis and diseases of the nervous system are further points to tell the prescriber about for tablets, liquid or suppositories
• In pregnancy the NHS says metronidazole may be possible but a doctor or pharmacist should be asked first, while MedlinePlus, a US source, says it generally should not be used in the first trimester
• The NHS says there is no evidence of an effect on fertility in men or women
• The Specialist Pharmacy Service says usual courses can be used during breastfeeding; the NHS asks for the baby to be watched, with contact with a healthcare professional or NHS 111 if the baby feeds poorly, has an upset stomach or has oral thrush, and MedlinePlus says a doctor may advise expressing and discarding milk
• The NHS says that if sickness or diarrhoea lasts more than 24 hours, the contraceptive pill may not protect against pregnancy

Interactions

Interactions documented in the official sources cited on each card. The list covers the medicines represented on this site and is not exhaustive; how the interaction data is compiled.

No pair records for this medicine are in the sources currently represented by Anatomy Nexus. Absence from this list does not mean no interaction exists.

Same-class and related medicines

Same class: Nitroimidazoles

Medicines that share the class of Metronidazole. They are separate medicines with their own licences, doses and interactions, not alternative names for Metronidazole.

Key facts

What is metronidazole used for?

Metronidazole is an antibiotic that the NHS describes as treating several bacterial infections. These include infections of the skin, rosacea, infections of the mouth such as infected gums and dental abscesses, bacterial vaginosis and pelvic inflammatory disease. It can also be used for infected insect bites, skin ulcers, bed sores and wounds. Trichomoniasis, a sexually transmitted infection, is treated with antibiotics, usually metronidazole. It comes as tablets, a liquid to drink, suppositories, skin gel, skin cream and vaginal gel. It can also be given by injection, but this is usually done only in hospital. For most infections, the NHS says people feel better within a few days.

How does metronidazole work?

Metronidazole is an antibiotic that treats bacterial and parasitic infections. It belongs to a group of medicines called nitroimidazole antimicrobials. Laboratory studies describe it as being switched on inside susceptible organisms, many of which live without oxygen. The switching-on pathways are absent in the aerobic cells of the human body, which helps explain why the medicine targets microbes. Once switched on, it forms short-lived products that bind to DNA and cause damage, including breaks in the DNA strands.

What are the side effects?

The NHS lists feeling or being sick, diarrhoea and a slight metallic taste in the mouth as common side effects of the tablets, liquid, suppositories and vaginal gel. Some people feel drowsy, so the NHS suggests checking reaction times before driving. Metronidazole gel or cream can cause dryness, itching or irritation of the skin. Serious side effects are rare and, according to the NHS, affect fewer than 1 in 1,000 people. Yellow skin or eyes, which the NHS links with liver or gallbladder problems, needs prompt contact with the GP or NHS 111. The NHS lists meningitis and brain disease as very rare serious side effects, and sudden serious symptoms of this kind are an emergency: call 999 or go to A&E. Swelling of the lips, mouth or throat, or trouble breathing, can signal a serious allergic reaction and also needs a 999 call. A hospital factsheet adds that numbness or tingling in the hands and feet can occur with longer courses, a reason to speak to the prescriber.

Metronidazole and alcohol

The NHS advises not drinking alcohol while taking metronidazole tablets or liquid or using suppositories. It says to keep avoiding alcohol for 2 days after treatment finishes, while the NHS trichomoniasis page gives at least 24 hours. The reason is that alcohol with metronidazole can cause feeling or being sick, stomach pain, hot flushes, palpitations and headache. The NHS also lists feeling unable to stop drinking alcohol during treatment among the reasons to talk to a doctor before using it. With the vaginal gel, the NHS says drinking can sometimes cause the same effects. MedlinePlus, a US source, gives a longer wait of at least 3 days after the last dose, so advice differs between publishers.

Who needs extra care?

The NHS page on who can take metronidazole mentions people who have ever had an allergic reaction to it or another medicine, people who are pregnant or breastfeeding, and people who are having blood tests. Liver problems, dialysis and diseases of the nervous system are further points to tell the prescriber about for tablets, liquid or suppositories. On pregnancy, the NHS says metronidazole may be an option but advises checking with a doctor or pharmacist first. It also says there is no evidence of an effect on fertility in men or women. The Specialist Pharmacy Service says usual courses can be used during breastfeeding, with the baby watched for poor feeding, stomach upset or oral thrush. The NHS says that if sickness or diarrhoea lasts more than 24 hours, the contraceptive pill may not protect against pregnancy.

Frequently asked questions