For oral administration. Metronidazole tablets should be swallowed, without chewing, with half a glassful of water during or after meals.

Prophylaxis against anaerobic infection:

Chiefly in the context of abdominal (especially colorectal) and gynaecological surgery.

Adults: 400 mg 8 hourly during 24 hours immediately preceding operation followed by postoperative intravenous or rectal administration until the patient is able to take tablets.

Children < 12 years: 20-30mg/kg as a single dose given 1-2 hours before surgery 

Treatment of established anaerobic infection:

Adults: 800 mg followed by 400 mg 8 hourly.

Children > 8 weeks to 12 years of age: The usual daily dose is 20-30 mg/kg/day as a single dose or divided into 7.5 mg/kg every 8 hours. The daily dose may be increased to 40 mg/kg, depending on the severity of the infection. Duration of treatment is usually 7 days.

Patients should be advised not to take alcohol during therapy and for at least 48 hours afterwards because of the possibility of a disulfiram-like (Antabuse effects) reaction. Psychotic reactions have been reported in patients who were using metronidazole and disulfiram concurrently.

Metronidazole can cause potentiation of anti-coagulant therapy when used with the Warfarin type oral anticoagulants. Dosage of the latter may require reducing. Prothrombin times should be monitored.

There is no interaction with heparin Lithium retention accompanied by evidence of possible renal damage has been reported in patients treated simultaneously with lithium and metronidazole. Lithium treatment should be tapered or withdrawn before administering Metronidazole. Plasma concentrations of lithium, creatinine and electrolytes should be monitored in patients under lithium treatment while receiving metronidazole.

Patients receiving phenobarbital or phenytoin metabolise metronidazole at a much greater rate than normal, reducing the half-life to approximately 3 hours. Metronidazole reduces the clearance of 5 fluorouracil, resulting in increased toxicity of 5 fluorouracil.

Patients receiving ciclosporin are at risk of elevated ciclosporin serum levels. Serum ciclosporin and serum creatinine should be closely monitored when coadministration is necessary. Plasma levels of busulfan may be increased by metronidazole which may lead to severe busulfan toxicity

Patients should be warned that metronidazole may darken urine.

Due to inadequate evidence on the mutagenicity risk in humans, the use of metronidazole for longer treatment than usually required should be carefully considered.

Cases of severe hepatotoxicity/acute hepatic failure, including cases with a fatal outcome with very rapid onset after treatment initiation in patients with Cockayne syndrome have been reported with products containing metronidazole for systemic use. In this population, metronidazole should therefore be used after careful benefit-risk assessment and if no alternative treatment is available. Liver function tests must be performed just prior to the start of the therapy, throughout and after end of treatment until liver function is within normal ranges, or until the baseline values are reached.

If the liver function tests become markedly elevated during treatment, the drug should be discontinued. Cases of severe bullous skin reaction such as Stevens Johnson syndrome (SJS), toxic epidermal necrolysis (TEN) or acute generalized exanthematous pustulosis (AGEP) have been reported with metronidazole. If symptoms or signs of SJS, TEN or AGEP are present, Metronidazole treatment must be immediately discontinued. Patients with Cockayne syndrome should be advised to immediately report any symptoms of potential liver injury to their physician and stop taking metronidazole. 

Contraindications 

Hypersensitivity to nitroimidazoles, metronidazole or any of the excipients

Precautions:

Metronidazole should be used with caution in patients with active or chronic severe peripheral and central nervous system disease due to the risk of neurological aggravation. The elimination half-life of metronidazole remains unchanged in the presence of renal failure. The dosage of metronidazole therefore needs no reduction. Such patients however retain the metabolites of Metronidazole. The clinical significance of this is not known at present. In patients undergoing haemodialysis, Metronidazole and metabolites are efficiently removed during an eight-hour period of dialysis. Metronidazole should therefore be re-administered immediately after haemodialysis. No routine adjustment in the dosage of metronidazole need to be made in patients with renal failure undergoing intermittent peritoneal dialysis (IDP) or continuous ambulatory peritoneal dialysis (CAPD). Metronidazole is mainly metabolised by hepatic oxidation. Substantial impairment of metronidazole clearance may occur in the presence of advanced hepatic insufficiency.