Mechanism of Action and Target
The antibiotic penetrates the microbial cell and disrupts translation. Its primary target is the 50S subunit of the bacterial ribosome.
- Biochemical effect: inhibition of the peptidyl transferase enzyme.
- Result: blocks the formation of peptide bonds between amino acids, completely halting the assembly of protein molecules.
An important feature of its pharmacodynamics is that the drug can also inhibit ribosomal function in human host cells, particularly in mitochondria. This exact property underlies its serious adverse effects.
Antimicrobial Spectrum and Indications
The drug possesses a broad spectrum of activity: it is effective against gram-positive and gram-negative microorganisms, including aerobic and anaerobic strains.
The most sensitive pathogens include:
- Haemophilus influenzae;
- Neisseria meningitidis;
- Pneumococci;
- Certain Bacteroides strains.
Due to significant toxicity, systemic use is strictly limited. Chloramphenicol is prescribed as a reserve drug only when safer alternatives have developed resistance or if other effective agents cause dangerous allergies in the patient. Main indications for systemic administration include typhoid fever, bacterial meningitis, and rickettsial infections.
Topically, the drug is used for skin conditions (furunculosis, trophic ulcers, infected burns, nipple fissures) and eye infections (conjunctivitis, keratitis, blepharitis).
Toxicity and Side Effects
Toxic reactions are rooted in the inhibition of mitochondrial protein synthesis. The most dangerous manifestations include:
- Gray baby syndrome. Occurs in newborns receiving high doses. Pathogenesis is driven by immature hepatic enzymes (lack of glucuronyl transferase conjugation), causing the drug to accumulate to toxic concentrations.
- Hematotoxicity.
- Reversible form: dose-dependent suppression of erythropoiesis.
- Irreversible form: aplastic anemia—a rare, potentially fatal idiosyncratic complication.
- Dyspepsia: frequent complaints of nausea, vomiting, and diarrhea.
Drug Interactions and Resistance
Bacteria develop resistance to chloramphenicol through two main mechanisms:
- Barrier mechanism: decreased permeability of the outer cell membrane to antibiotic molecules.
- Enzymatic mechanism: plasmid-mediated transfer of genetic information for special acetyltransferases that inactivate the drug.
Pharmacokinetic interactions: By inhibiting hepatic microsomal enzymes, chloramphenicol slows the clearance of drugs such as phenytoin and warfarin. This increases their half-life ($t_{1/2}$) and raises the risk of toxicity.
Pharmacodynamic interactions: As a bacteriostatic agent, chloramphenicol can antagonize the efficacy of bactericidal antibiotics (e.g., penicillins and aminoglycosides), whose action depends directly on active cell division.