Metronidazole

Metronidazole is an antibiotic that is active against anaerobic bacteria and certain parasites. It is used to treat trichomoniasis, bacterial vaginosis (Gardnerella infection), amebic infections, and anaerobic bacterial infections.

For sexually transmitted infections, metronidazole works against Trichomonas vaginalis – a single-celled parasite that causes vaginal infections and urethritis.

The medication is available as tablets and as a vaginal gel/ovules.

Metronidazole acts against organisms that live in the absence of oxygen:

Mechanism of action: Inside the target organisms, metronidazole is converted into reactive intermediates. These damage the DNA of the pathogens and lead to cell death.

Spectrum of activity:

• Trichomonas vaginalis (parasite)
• Anaerobic bacteria (e.g., Gardnerella, Bacteroides)
• Giardia lamblia
• Entamoeba histolytica

Special feature: The prodrug must first be activated by enzymes of the microorganisms. Only anaerobic pathogens have these enzymes – which is why metronidazole acts very selectively.

Metronidazole is suitable for:

• Trichomoniasis (Trichomonas infection)
• Bacterial vaginosis
• Anaerobic infections
• As part of H. pylori eradication

Most common STI uses:

• Trichomoniasis: single dose or 7-day therapy
• Bacterial vaginosis: 7-day therapy, oral or vaginal

Not suitable in cases of:

• 1st trimester of pregnancy
• During alcohol consumption
• Severe liver disease
• Neurological disorders

For trichomoniasis:

• 2 g as a single dose OR
• 400-500 mg twice daily for 7 days

For bacterial vaginosis:

• 400-500 mg twice daily for 7 days OR
• 2 g single dose (lower efficacy) OR
• Vaginal gel (0.75%) once daily for 5 days

Available forms:

• Tablets 250 mg, 400 mg, 500 mg
• Vaginal gel 0.75%
• Vaginal suppositories 500 mg

Tablets:

• Take with or after a meal
• Swallow with a glass of water
• Stick to the prescribed duration

Vaginal forms:

• Insert in the evening before going to bed
• Use the applicator as described in the package leaflet
• No tampons during treatment

Strict rule: NO ALCOHOL! Do not drink alcohol during treatment and for 48 hours afterward. The combination causes severe nausea, vomiting, and headache (disulfiram-like reaction).

Partner treatment: In trichomoniasis, the partner must always be treated as well.

Metronidazole must not be taken in cases of:

• Hypersensitivity to metronidazole or nitroimidazoles
• 1st trimester of pregnancy
• Neurological disorders with a tendency to seizures

Absolute prohibition:

• Alcohol consumption during therapy

Caution in cases of:

• 2nd and 3rd trimesters of pregnancy
• Breastfeeding (single dose possible, followed by a 12-24 hour break from breastfeeding)
• Liver disease
• Disorders of blood formation

Pregnancy: In the 1st trimester, only if vitally indicated. In the 2nd/3rd trimester, metronidazole can be used for trichomoniasis.

Common (1-10%):

• Nausea
• Metallic taste in the mouth
• Headache
• Loss of appetite
• Abdominal pain

Uncommon (0.1-1%):

• Diarrhea
• Vomiting
• Dry mouth
• Dizziness
• Darkening of the urine

Rare:

• Peripheral neuropathy (tingling in hands/feet)
• Seizures
• Changes in blood count

Disulfiram reaction: With alcohol consumption: severe nausea, vomiting, flushing, headache, racing heart. Can be life-threatening.

Avoid completely:

• Alcohol (for at least 48 hours after the last dose)
• Disulfiram (psychotic reactions possible)

Interactions with:

• Warfarin – increased tendency to bleed (INR monitoring)
• Lithium – increased lithium levels
• Phenytoin – altered levels of both medications
• Cyclosporine – increased cyclosporine toxicity

No relevant effect:

• Hormonal contraception (with short-term use)