Common indications: Treatment of infections caused by anaerobic bacteria in:
1. Antibiotic-associated colitis caused by Clostridium difficile, which is a Gram-positive anaerobe.
2.Oral infections (such as dental abscess) or aspiration pneumonia caused by Gram-negative anaerobes from the mouth.
3.Surgical and gynaecological infections caused by Gram-negative anaerobes from the colon, for example Bacteroides fragilis.
4. Also effective for treatment of protozoal infections including trichomonal vaginal infection, amoebic dysentery, giardiasis.
Prescription: Metronidazole is available in a variety of formulations. The oral route is used for gastrointestinal infection or where the patient is not systemically unwell. A typical starting dose would be 400 mg orally 8-hrly. The intravenous route, usually at a dose of 500 mg IV 8-hrly, is used for severe infection or where patients cannot take treatment by mouth. Rectal metronidazole is an alternative for patients who are nil by mouth. Metronidazole can be prescribed as a gel for topical administration to treat vaginal infection such as bacterial vaginosis or to reduce the odour from an infected skin ulcer.
Administration: Oral metronidazole may be taken as tablets or in an oral suspension. Intravenous metronidazole is given as an infusion over 20 minutes.
Communication: Explain that the aim of treatment is to get rid of infection and improve symptoms. For oral treatment, encourage the patient to complete the prescribed course. Before prescribing, always check with your patient personally or get collateral history to ensure that they have no allergy to metronidazole. Warn the patient not to take alcohol during or for 48 hours after treatment, explaining that if they do they may feel very unwell
with nausea, vomiting, flushing and headache. If an allergy develops during treatment, give the patient written and verbal advice not to take this antibiotic in the future and make sure that the allergy is clearly documented in their medical records.
Monitoring: Check that infection resolves by review of symptoms, signs and blood tests (improvement in inflammatory markers) if appropriate. For treatment exceeding 10 days, measure full blood count and liver function tests to monitor for adverse effects.