Chloramphenicol
A broad-spectrum antibiotic capable of crossing the corneal barrier and entering the anterior chamber. * **Susceptible Organisms:** Typically effective against *Staphylococcus* spp. and *Streptococcus* spp. * **Resistant Organisms:** *Pseudomonas* spp. are generally resistant. * **Clinical Use:** Useful in treating cats with suspected *Mycoplasma* or chlamydial conjunctivitis. It is one of the few commercially available ophthalmic antibiotics in ointment form. * **Safety Note:** Its use in veterinary ophthalmology is becoming less widespread due to the potential for severe toxicity (aplastic anemia) in humans handling the drug.
Mechanism: Chloramphenicol is a bacteriostatic antibiotic that inhibits bacterial protein synthesis. It binds reversibly to the **50S ribosomal subunit** of susceptible organisms โ prevents the binding of aminoacyl tRNA to the ribosome โ inhibits peptide bond formation via **peptidyl transferase**.
Dosing by species
- Established corneal infection ยท One drop or 1/4 inch strip ยท topical ophthalmic ยท up to hourly ยท Application may be very frequent for established infections.
- Ophthalmic infections ยท 1 drop (solution) or ointment ยท topical ยท q4-8h (solution); q8-12h (ointment) ยท Not specified ยท High lipid solubility makes it suitable for intraocular infections.
- Systemic infections ยท 40-50 mg/kg ยท IV/IM/SC/PO ยท q8h ยท Not specified ยท Restrict to life-threatening infections resistant to other antimicrobials.
- CNS infections ยท 10-15 mg/kg ยท PO ยท q4-6h ยท Not specified ยท Recommended in some texts for CNS penetration.
- Prophylaxis following surgery or Mycoplasma/chlamydial conjunctivitis ยท One drop (or 1/4 inch strip if using ointment) ยท topical ophthalmic ยท q6h (four times daily) ยท Up to 21 days ยท Labels state to not use longer than 7 days in cats, but three times daily application of ointment for 21 days to cats did not cause toxicity.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Food-producing animals
- Known hypersensitivity to chloramphenicol
Adverse effects
- Fatal aplastic anemia in humans (exposure risk)
- Local irritation (rare)
Drug interactions
- Pentobarbital ยท Irreversible inhibition of hepatic cytochrome P450 increases plasma levels of pentobarbital. Recovery takes up to 3 weeks. ยท major
- Phenobarbital ยท Irreversible inhibition of hepatic cytochrome P450 increases plasma levels of phenobarbital. Recovery takes up to 3 weeks. ยท major
- Propofol ยท Irreversible inhibition of hepatic cytochrome P450 increases plasma levels of propofol. Recovery takes up to 3 weeks. ยท major
- Oral hypoglycaemic agents ยท Irreversible inhibition of hepatic cytochrome P450 increases plasma levels of hypoglycaemics. ยท major
- Rifampin ยท Accelerates the metabolism of chloramphenicol, decreasing serum levels. ยท moderate
- Aminoglycosides ยท Chloramphenicol may inhibit the bactericidal activity of aminoglycosides. ยท moderate
- Beta-lactams ยท Chloramphenicol may inhibit the bactericidal activity of beta-lactams. ยท moderate
- Macrolides ยท May competitively inhibit macrolide antimicrobials at the 50S ribosomal subunit. ยท moderate
- Lincosamides ยท May competitively inhibit lincosamide antimicrobials at the 50S ribosomal subunit. ยท moderate
Monitoring
- Resolution of clinical signs of conjunctivitis/keratitis
- Owner compliance with safety protocols (glove use)
Overdose
Topical ophthalmic overdose is unlikely to cause systemic toxicity in the animal, but prolonged use may disrupt normal ocular flora.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.