Metronidazole

How it works

Within susceptible anaerobic organisms metronidazole is reduced to reactive intermediates that damage microbial DNA, producing a bactericidal effect; it is also active against certain protozoa.

Prescribing in practice

• Avoid alcohol during treatment and for a short period afterwards because of the risk of a disulfiram-like reaction (flushing, nausea, vomiting, tachycardia).
• It potentiates the effect of warfarin and can raise lithium levels, and prolonged or repeated courses carry a risk of peripheral and central neuropathy.
• Dosing should be reviewed in significant hepatic impairment, where clearance is reduced.

Monitoring

Monitor INR closely if the patient is on warfarin, and watch for neurological symptoms with prolonged courses.

Counselling the patient

• Do not drink any alcohol while taking this and for a couple of days after finishing.
• Complete the full course even if you feel better.
• Report numbness, tingling in the hands or feet, or unsteadiness.

Evidence & guidelines

Metronidazole is the long-established standard agent for anaerobic infection, with its indications, interactions and cautions set out in the SPC and current prescribing references.