Metronidazole

O que é Metronidazole?

Metronidazole is an antibiotic and antiprotozoal medicamento that is the first-line tratamento for bacterial vaginosis (BV) and trichomoniasis in Europe, as recommended by the WHO and European STI tratamento guidelines. It is also used as part of combination regimens for pelvic inflammatory disease (PID) and for various other anaerobic bacterial infections.

Metronidazole is listed on the WHO Model List of Essential Medicines and has been in clinical use since the 1960s. It is available in oral comprimido, vaginal gel, and topical creme formulations, allowing flexible tratamento approaches depending on the condition and paciente preference.

Como funciona Metronidazole work?

Metronidazole is a nitroimidazole antibiotic that works through a unique mechanism targeted at anaerobic organisms:

1. Intracellular activation: Metronidazole enters bacterial and protozoal cells. In anaerobic organisms (which lack oxygen), the nitro group of metronidazole is reduced by intracellular electron transport proteins (ferredoxins) to form a reactive intermediate.
2. DNA damage: The reactive intermediate binds to and damages bacterial and protozoal DNA, causing strand breaks and preventing normal function.
3. Selective toxicity: This reduction and activation process occurs primarily in anaerobic and microaerophilic organisms. Human aerobic cells do not reduce metronidazole in the same way, giving the drug its selective activity against anaerobes and protozoa with minimal harm to normal human cells.

This mechanism explains why metronidazole is highly effective against:

• Anaerobic bacteria: Including Gardnerella vaginalis, Prevotella spp., Mobiluncus spp. (key organisms in bacterial vaginosis)
• Protozoa: Trichomonas vaginalis (trichomoniasis), Giardia lamblia, Entamoeba histolytica

Para quem é Metronidazole for?

Primary sexual health indications:

• Bacterial vaginosis (BV): First-line tratamento — oral metronidazole 400–500 mg twice daily for 5–7 days, or metronidazole vaginal gel 0.75% once daily for 5 days
• Trichomoniasis: Single oral dose of 2 g (or 400–500 mg twice daily for 5–7 days) — partner tratamento is essential as trichomoniasis is sexually transmitted
• Pelvic inflammatory disease (PID): Used in combination with other antibiotics as part of multi-drug regimens

Other uses:

• Dental and oral anaerobic infections
• Abdominal and pelvic anaerobic infections
• Clostridioides difficile infection (oral)

Metronidazole is not effective against:

• Viral infections (herpes, HPV, HIV)
• Aerobic bacteria (standard bacterial infections — use appropriate antibiotics)
• Fungal infections (use antifungals such as clotrimazole or fluconazole)
• Chlamydia or gonorrhoea (different antibiotics are required)

Dosagem

Indication	Dose	Duration
Bacterial vaginosis (oral)	400–500 mg twice daily	5–7 days
Bacterial vaginosis (vaginal gel 0.75%)	1 applicatorful per night	5 nights
Trichomoniasis (standard)	400–500 mg twice daily	5–7 days
Trichomoniasis (single dose)	2 g single dose	1 day
PID (in combination)	400 mg twice daily	14 days

Oral metronidazole should be taken with food to reduce gastrointestinal efeito secundários. Alcohol must be completely avoided during tratamento and for 48 hours after completion.

Efeitos secundários

Very common efeito secundários

• Nausea
• Metallic taste in the mouth (very characteristic of metronidazole)

Efeitos secundários comuns

• Vomiting
• Abdominal discomfort or cramping
• Diarrhoea
• Loss of appetite
• Headache
• Dizziness

Menos comuns efeito secundários

• Dark or brownish urine (harmless discolouration from metronidazole metabolites)
• Dry mouth
• Tongue discomfort, furring of the tongue
• Peripheral neuropathy: Tingling, numbness, or weakness in the hands or feet — report to a médico if this occurs; tratamento may need to be stopped

Rare but serious efeito secundários

• Disulfiram-like reaction with alcohol: Severe flushing, nausea, vomiting, tachycardia — alcohol must be strictly avoided
• Seizures and encephalopathy: Rare; more likely with high doses or prolonged tratamento
• Leucopenia: Reduced white blood cells — usually reversible
• Serious allergic reactions: Including angioedema and anaphylaxis

Metronidazole vs alternativas for bacterial vaginosis

Treatment	Route	Duration	Notes
Metronidazole (oral)	Oral comprimido	5–7 days	First-line; systemic tratamento
Metronidazole (vaginal)	Vaginal gel	5 nights	Local tratamento; lower systemic efeito secundários
Clindamycin (vaginal)	Vaginal creme	7 nights	Alternative; may disturb condom efficacy
Clindamycin (oral)	Oral	7 days	Alternative if oral preferred

Metronidazole vs vaginal metronidazole gel: Both are effective for BV. Vaginal gel delivers medicamento directly to the infection site with lower systemic exposure, potentially causing fewer gastrointestinal efeito secundários and avoiding the alcohol interaction to some degree. The oral route treats the systemic bacterial load and may be more appropriate in some clinical situations.

Como aceder a Metronidazole online na Europa

Metronidazole is a medicamento sujeito a receita médica (POM) in most estados-membros da UE. It cannot legally be dispensed without a valid receita médica from a licensed medical professional.

Prescrivia operates as a technology intermediary: we do not prescribe medicamentos, employ médicos, or sell medicamentos. Our platform connects pacientes with independent EU-registered médicos who can conduct confidential online health assessments.

The process:

1. Complete uma avaliação de saúde: Describe your symptoms (discharge, odour, itching), relevant sexual history, and any current medications.
2. Avaliação médica: An independent EU-registered médico reviews your assessment. If metronidazole is clinically appropriate, they may issue a receita médica.
3. Dispensa na farmácia: The receita médica is sent to a licensed EU farmácia partner for dispensing and direct delivery.

Important: A Prescrivia não garante that a receita médica will be issued. All prescribing decisions are made independently by qualified medical professionals.

Informação de segurança importante

Do not take Metronidazole if you:

• Are in the first trimester of pregnancy (avoid if possible — discuss with médico for second/third trimester)
• Are breastfeeding (if a single high dose is used, breastfeeding should be interrupted for 12–24 hours)
• Are allergic to metronidazole or other nitroimidazole medicamentos (tinidazole, ornidazole)

Informe o seu médico before taking Metronidazole if you:

• Have liver disease (dose reduction or increased monitoring may be required)
• Have a history of neurological conditions or seizures
• Are taking warfarin (metronidazole significantly increases anticoagulant effect — INR monitoring is required)
• Are taking lithium (metronidazole can raise lithium levels)
• Are taking disulfiram (do not use together — risk of psychotic reactions)

Recurrent BV: Bacterial vaginosis frequently recurs after tratamento. If you experience multiple episodes, a médico should investigate contributing factors such as sexual practices, hygiene, hormonal factors, and the potential role of suppressive vaginal gel regimens.

Trichomoniasis — treat partners: Trichomoniasis is a sexually transmitted infection and partners must be treated simultaneously to prevent reinfection, regardless of whether they have symptoms.

Fontes

Medical information on this page is based on the following sources:

• Organização Mundial da Saúde (WHO). WHO Guidelines for the Treatment of Trichomonas vaginalis. 2016. who.int
• European STI Guidelines Editorial Board. 2018 European guideline on the management of vaginal discharge. Journal of the European Academy of Dermatology and Venereology.
• Organização Mundial da Saúde (WHO). WHO Model List of Essential Medicines. 22nd edition, 2021.
• Agência Europeia de Medicamentos (EMA). Metronidazole — Summary of Product Characteristics. Available at: ema.europa.eu

This content is reviewed periodically to reflect updated clinical guidance. It is provided for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for advice relevant to your individual health circumstances.