Chloramphenicol

Chloramphenicol is a broad-spectrum antibiotic produced by actinobacteria of the genus Streptomyces. It exerts its effect by binding to the 50S subunit of the bacterial ribosome and inhibiting peptidyl transferase, thereby blocking protein synthesis. It is generally considered bacteriostatic, though it can be bactericidal against some organisms at high concentrations.

It is active against a wide range of organisms, including many Gram-positive cocci and Gram-negative bacilli, as well as rickettsiae, chlamydiae, and some anaerobes. It is not reliably active against Pseudomonas aeruginosa, and resistance exists in some species. Its ability to penetrate the cerebrospinal fluid makes it useful for certain meningitis cases.

Systemic chloramphenicol is reserved for serious infections where safer alternatives are not suitable—for example, certain typhoid and other systemic infections, and selected rickettsial diseases. It remains in use in some settings due to low cost and availability, particularly in resource-limited regions. Topical ophthalmic formulations are used for conjunctival infections and other superficial ocular conditions.

Chloramphenicol is well absorbed orally and distributes widely, including into the central nervous system. It is mainly metabolized by hepatic glucuronidation and excreted in urine. Adverse effects include dose-related bone marrow suppression and a rare but irreversible aplastic anemia; a particularly feared event is Gray baby syndrome in neonates, due to immature glucuronidation. Because of these risks, use is carefully weighed against alternatives.

Resistance can occur via chloramphenicol acetyltransferase–mediated inactivation and reduced uptake. Because of toxicity risks, chloramphenicol use is restricted in many countries, and its use in food-producing animals is prohibited or heavily restricted to prevent residues and resistance.