Metronidazole
2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethanol

Absorption
Oral metronidazole is well absorbed; topical application is less complete and more prolonged. Following administration, T max is 1 to 2 h, and C max is 25 mg/mL. Oral bioavailability is not affected by food, but peak serum levels will be delayed to 2 h.

Distribution
Metronidazole appears in cerebrospinal fluid, saliva, and breast milk in concentrations similar to those found in plasma. Less than 20% is protein bound.

Metabolism
Metabolites are 2–hydroxymethyl and acidic metabolite.

Elimination
Routes of elimination are via urine (60% to 80%) and feces (6% to 15%). Renal Cl is approximately 10 mL/min per 1.73 m 2 . The t ½ is 8 h in healthy adults, and the hydroxy-metabolite t ½ is 15 h.

Special Populations
Hepatic Function Impairment
Patients with hepatic function impairment metabolized metronidazole slower; accumulation of drug may occur. Cautiously administer doses below the usual recommended dose.

Elderly
Because the pharmacokinetics of metronidazole may be altered in the elderly, monitoring of serum levels may be necessary to adjust the dosage accordingly.

Anticoagulants
Anticoagulant effect may be increased.

Barbiturates, phenytoin
Therapeutic failure of metronidazole may occur.

Cimetidine
May prolong the t ½ and decrease plasma Cl of metronidazole.

Disulfiram
Concurrent use may result in acute psychosis or confusional state. Do not give metronidazole to patients who have taken disulfiram within last 2 wk.

Ethanol
Disulfiram-like reaction including flushing, palpitations, tachycardia, nausea, and vomiting may occur with concurrent use.

Lithium
Plasma levels may be elevated by metronidazole, increasing the risk of lithium toxicity.