Clinical Pharmacokinetics of Chloramphenicol and Chloramphenicol Succinate

In recent years there has been a renewal of interest in chloramphenicol, predominantly because of the emergence of ampicillin-resistant Haemophilus influenzae, the leading cause of bacterial meningitis in infants and children. Three preparations of chloramphenicol are most commonly used in clinical practice: a crystalline powder for oral administration, a palmitate ester for oral administration as a suspension, and a succinate ester for parenteral administration. Both esters are inactive, requiring hydrolysis to chloramphenicol for anti-bacterial activity. The palmitate ester is hydrolysed in the small intestine to active chloramphenicol prior to absorption. Chloramphenicol succinate acts as a prodrug, being converted to active chloramphenicol while it is circulating in the body. Various assays have been developed to determine the concentration of chloramphenicol in biological fluids. Of these, high-performance liquid chromatographic and radioenzymatic assays are accurate, precise, specific, and have excellent sensitivities for chloramphenicol. They are rapid and have made therapeutic drug monitoring practical for chloramphenicol. The bioavailability of oral crystalline chloramphenicol and chloramphenicol palmitate is approximately 80%. The time for peak plasma concentrations is dependent on particle size and correlates with in vitro dissolution and deaggregation rates. The bioavailability of chloramphenicol after intravenous administration of the succinate ester averages approximately 70%, but the range is quite variable. Incomplete bioavailability is the result of renal excretion of unchanged chloramphenicol succinate prior to it being hydrolysed to active chloramphenicol. Plasma protein binding of chloramphenicol is approximately 60% in healthy adults. The drug is extensively distributed to many tissues and body fluids, including cerebrospinal fluid and breast milk, and it crosses the placenta. Reported mean values for the apparent volume of distribution range from 0.6 to 1.0 L/kg. Most of a chloramphenicol dose is metabolised by the liver to inactive products, the chief metabolite being a glucuronide conjugate; only 5 to 15% of chloramphenicol is excreted unchanged in the urine. The elimination half-life is approximately 4 hours. Inaccurate determinations of the pharmacokinetic parameters may result by incorrectly assuming rapid and complete hydrolysis of chloramphenicol succinate. The pharmacokinetics of chloramphenicol succinate have been described by a 2-compartment model. The reported values for the apparent volume of distribution range from 0.2 to 3.1 L/kg.(ABSTRACT TRUNCATED AT 400 WORDS)