amphenicol

Amphenicol is a class of broad-spectrum antibiotics that inhibit bacterial protein synthesis by binding to the 50S ribosomal subunit, thereby blocking peptidyl transferase. The best-known member is chloramphenicol; related derivatives include thiamphenicol and florfenicol.

Amphenicols are active against a wide range of bacteria, including many Gram-positive and Gram-negative species, as well as intracellular organisms such as rickettsiae and chlamydiae. They were historically used for severe infections such as meningitis and typhoid fever when other agents were unavailable. In modern clinical practice human use is limited due to safety concerns; they may be used in selected cases where alternative therapies are ineffective. In veterinary medicine they are used in some countries under strict regulatory controls.

Chloramphenicol is well absorbed orally and distributes widely, including the central nervous system. It is primarily metabolized in the liver by glucuronidation and excreted in urine. Thiamphenicol has similar distribution with somewhat different metabolism.

Adverse effects include dose-independent bone marrow suppression, which can lead to aplastic anemia, a rare but potentially fatal complication. Gray baby syndrome may occur in neonates due to immature drug conjugation. Other risks include hypersensitivity reactions and interactions with other marrow-suppressing drugs. Because of these hazards, use is generally restricted, and patients are monitored with blood counts when therapy is given, with avoidance in pregnancy and lactation in many jurisdictions.

Resistance commonly arises via chloramphenicol acetyltransferase, which inactivates the drug, or from decreased uptake. Regulatory policies restrict human use and limit or prohibit use in food-producing animals to curb toxicity risks and resistance spread.