Metronidazole

How it works

It is reduced intracellularly by anaerobic organisms to reactive nitroso intermediates that cause DNA strand breakage and bacterial cell death, giving it selective activity against anaerobes and microaerophiles.

Prescribing in practice

• Warn patients to avoid alcohol during treatment and for a short period afterwards because of a potential disulfiram-like reaction with flushing, nausea and vomiting.
• It potentiates warfarin and other coumarin anticoagulants, so monitor INR closely when co-prescribed.
• Prolonged or high-dose courses carry a risk of peripheral and central neuropathy, so avoid unnecessarily long treatment.

Monitoring

For short courses no routine monitoring is needed, but check for neurological symptoms during prolonged therapy and monitor INR in patients taking anticoagulants.

Counselling the patient

• Do not drink alcohol while taking this medicine and avoid it for a couple of days after finishing the course.
• Complete the full course even if you feel better.
• Report any numbness, tingling or unsteadiness, which should be reviewed.

Evidence & guidelines

Metronidazole is established UK standard-of-care for anaerobic and protozoal infections and features in NICE and national antimicrobial guidance.