<p>In vitro, chloramphenicol exerts mainly a bacteriostatic effect on a wide range of Gram-negative and Gram positive bacteria and is active against rickettsiae, the lymphogranuloma-psittacosis group and Vibrio cholerae. It is particularly active against Salmonella typhi and Haemophilus influenzae. The mode of actions is through interference or inhibition of protein synthesis in intact cells and cell-free systems. Antagonism has been demonstrated in vitro between chloramphenicol, erythromycin, clindamycin and lincomycin. Chloramphenicol is rapidly absorbed from the GI tract. Chloramphenicol palmitate is hydrolyzed in the GI tract and is absorbed as free chloramphenicol.<br />
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Following oral administration of a single one gram dose of chloramphenicol base to healthy adults, average peak plasma chloramphenicol concentrations of about 11 mcg/ml were attained with 1-3 hours. Cumulative dosing gave a peak of 18 mcg/ml after the fifth dose of one gram, every 6 hours. Mean serum levels were 8-14 mcg/ml over a 48 hour period.<br />
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Most of the drug is excreted in the urine. Despite the small proportion of unchanged drug excreted in the urine, the concentration of free chloramphenicol in the urine is relatively high. From 8% to 12% of the antibiotic is excreted as free chloramphenicol. The remainder is excreted as inert metabolites, mainly glucuronate. Small amounts of active drug are found in bile and feces. Chloramphenicol diffuses rapidly, but its distribution is not uniform. Highest concentrations are found in liver and kidney, and lowest concentrations are found in brain and cerebrospinal fluid (CSF). Chloramphenicol enters CSF even in the absence of meningeal inflammation, appearing in concentrations about half of those found in the blood.</p>