Adults

Typical adult dosage for most infections: 500 mg every 8 hours for 7-10 days. For syrup (200mg/5ml), this would be 12.5 ml every 8 hours. Dosage varies by infection.

Elderly

Use with caution. Dosage adjustments may be necessary due to decreased hepatic function. Generally, start with the lowest effective dose.

Children

Typical pediatric dosage for amebiasis: 35-50 mg/kg/day divided into 3 doses for 5-10 days (max 2250 mg/day). For giardiasis: 15 mg/kg/day divided into 3 doses for 5-7 days (max 750 mg/day). Dosage is highly dependent on weight and type of infection.

Renal_impairment

No dosage adjustment needed for mild to moderate renal impairment. For severe renal impairment or end-stage renal disease, dose reduction or extended dosing interval may be required.

Onset

Clinical effects may be observed within hours to days, depending on the infection type.

Excretion

Primarily renal (60-80% as metabolites and unchanged drug); about 6-15% is excreted in feces.

Half life

Approximately 8 hours (range 6-12 hours).

Absorption

Rapid and almost complete absorption after oral administration. Peak plasma concentrations usually occur within 1-2 hours.

Metabolism

Extensively metabolized in the liver by oxidation with side-chain reduction and glucuronide conjugation. The main metabolite is 2-hydroxymethyl metronidazole.

Alcohol

Disulfiram-like reaction (abdominal cramps, nausea, vomiting, headache, flushing).

Lithium

Increased serum lithium levels, leading to toxicity.

Cimetidine

May prolong metronidazole half-life, increasing its concentration.

Disulfiram

Psychotic reactions if taken concurrently or within 14 days.

Phenobarbital/Phenytoin

May reduce metronidazole plasma levels by increasing metabolism.

Warfarin and other oral anticoagulants

Potentiates anticoagulant effect, requiring dose adjustment and increased INR monitoring.