Chloramphenicol is metabolized in the liver, mainly by conjugation with glucuronic acid; only about 5 to 15% of an oral dose is excreted unchanged in the urine. The half-life of chloramphenicol is 1.5 to 4 hours in adults with normal renal and hepatic function. The plasma half-life is increased in patients with markedly reduced hepatic function. In patients with impaired renal function, the half-life of chloramphenicol itself is not significantly altered although the half-life of the inactive metabolites may be prolonged. Following i.v. administration, patients with renal impairment may achieve higher chloramphenicol concentrations due to decreased renal excretion of the succinate ester.
Since the processes for glucuronide conjugation and renal excretion in neonates may be immature, the half-life of the drug in neonates less than 3 days old may be in excess of 24 hours and about 10 hours for infants 10 to 16 days old. In these cases the dosage and administration interval should be adjusted using measured serum concentrations.