Metronidazole

Treatment for bacterial vaginosis with metronidazole

Metronidazole 400mg tablets are a prescription-only antibiotic most commonly used to treat bacterial vaginosis (BV), a common imbalance of the natural bacteria in the vagina. Metronidazole belongs to the nitroimidazole class of anti-infective medicines and is supplied as the generic drug, in a standard pack size, following an online consultation. This page focuses on its use for BV; metronidazole also treats other bacterial and protozoal infections, but the dose and course length for those can differ from the BV regimen described here.

Access metronidazole following an online medical consultation

Start the online consultation and complete the medical questionnaire. A UK-registered prescriber will review your answers and, where appropriate, issue a prescription for metronidazole 400mg tablets.

What is bacterial vaginosis?

BV happens when the natural balance of bacteria in the vagina is disrupted, allowing bacteria such as Gardnerella vaginalis to outnumber the protective Lactobacilli that normally keep the vaginal environment slightly acidic. It's the most common cause of unusual vaginal discharge in women of reproductive age: typically a thin, greyish-white discharge with a fishy odour, often more noticeable after sex or a period. BV doesn't usually cause soreness or itching in the way thrush does.

BV is not classed as a sexually transmitted infection, although it's more common in women who are sexually active. Because its symptoms can overlap with thrush, trichomoniasis, and some STIs, a degree of diagnostic uncertainty is normal. Your UK-registered prescriber may recommend an STI test, particularly if you have new or multiple partners, or an in-person examination and swab if your symptoms are atypical, persistent, or you are pregnant.

How metronidazole works and the BV regimen

Metronidazole is absorbed into anaerobic bacterial cells, where it disrupts their DNA and prevents them from multiplying. As these bacteria clear, the vagina's natural Lactobacilli can re-establish themselves, helping restore a healthy balance.

Your prescriber will select one of two recognised dosing options for BV: 

• 400mg twice daily for 5 to 7 days, taken during or just after food, or
• A single 2g dose (5 x 400mg tablets, taken together)

Your prescriber will confirm which regimen has been prescribed; the two aren't interchangeable, so follow the course length and timing set out for you rather than general information found elsewhere. There is no single universal dose for metronidazole across all infections.

Tablets should be swallowed whole with water, not crushed or chewed. Complete the full course even if symptoms improve early, as stopping prematurely makes recurrence more likely. If you miss a dose, take it as soon as you remember unless it's nearly time for the next one, in which case skip it; never double up. Metronidazole is prescribed for you specifically and shouldn't be shared.

Alcohol warning

Do not drink alcohol while taking metronidazole and for at least 48 hours after your last dose. Metronidazole can interfere with how the body breaks down alcohol, producing a disulfiram-like reaction, with symptoms including flushing, nausea, vomiting, and a fast heartbeat. This is a well-documented effect, so it's worth being mindful of alcohol in food, mouthwash, or other products during this window too.

Who should take extra care, or avoid metronidazole

Tell your prescriber your full medical history before starting, including if you:

• Are pregnant or trying to conceive: not recommended in the first trimester, used later in pregnancy only if necessary
• Are breastfeeding: single high-dose treatment usually requires pausing breastfeeding for 12 to 24 hours
• Have liver disease, or a history of seizures or other neurological problems
• Have Cockayne syndrome: rare but serious cases of severe liver injury have been reported in this group; used only if no alternative is suitable, with close liver monitoring
• Are older or frail, as you may be more susceptible to side effects

Interactions to be aware of

Metronidazole can interact with warfarin and other oral anticoagulants (bleeding risk may increase), lithium (levels may rise), disulfiram (risk of psychiatric reactions), certain anti-seizure medicines such as phenytoin and phenobarbital, and cimetidine and busulfan. This isn't a complete list, so always tell your prescriber about everything you take, so they can screen for interactions.

Side effects

Common side effects (may affect up to 1 in 10 people) include nausea, a metallic taste, diarrhoea, and headache.

Seek urgent medical attention for a severe rash or allergic reaction, jaundice, confusion, seizures, numbness or tingling suggestive of nerve problems, or unusual bruising or bleeding that could indicate a blood disorder. These are rare but recognised effects and should be reported promptly.

What to expect and follow-up

Most people notice symptoms improving within a few days. BV can recur even after successful treatment; if this happens, your prescriber may discuss alternatives such as vaginal metronidazole gel or clindamycin cream, or review contributing factors. As BV isn't an STI, routine partner treatment isn't recommended by UK guidance, though your prescriber can advise if your circumstances differ.

How to get metronidazole through DoktorABC

• Complete medical questionnaire: Start your online consultation and answer a series of health questions about your symptoms and medical history.
• Prescriber review: A UK-registered prescriber reviews your answers and, if treatment is considered appropriate, approves a prescription online.
• Delivery: Your medication is dispensed by a GPhC-registered pharmacy and delivered to your door in discreet packaging.

Metronidazole PIL, available via the Electronic Medicines Compendium (eMC): https://www.medicines.org.uk/emc/files/pil.12817.pdf

This page is general information only and does not replace the PIL or individual medical advice.