Chlortetracycline
Also known as: Aureomycin · Pennchlor · CTC · CLTC 100 MR · Ophtocycline · clortetraciclina · A-377 · NRRL2209 · SF-66 · Chlortetracycline hydrochloride
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections | 25 mg/kg PO q6-8h | PO | q6-8h | — | 🌎 NA |
| Bacterial conjunctivitis, keratitis, blepharitis, and spontaneous chronic corneal epithelial defects (SCCEDs) | 0.5-2 cm of ointment to affected eye | topical | q6h | 5 days | 🌍 EU |
- Bacterial conjunctivitis, keratitis, blepharitis, and spontaneous chronic corneal epithelial defects (SCCEDs): Used for immunomodulatory mechanism in SCCEDs.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections | 25 mg/kg PO q6-8h | PO | q6-8h | — | 🌎 NA |
| To prevent recurrence of mycoplasma or chlamydial conjunctivitis in large catteries | 50 mg per day per cat | PO | q24h | 1 month | 🌎 NA |
| Feline chlamydial conjunctivitis, mycoplasmal conjunctivitis, bacterial keratitis/blepharitis | 0.5-2 cm of ointment to affected eye | topical | q6h | 5 days | 🌍 EU |
- To prevent recurrence of mycoplasma or chlamydial conjunctivitis in large catteries: Administer soluble chlortetracycline powder in food.
- Feline chlamydial conjunctivitis, mycoplasmal conjunctivitis, bacterial keratitis/blepharitis: Oral doxycycline is the treatment of choice for feline chlamydial conjunctivitis.
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections (Rabbits) | 50 mg/kg PO q12-24h | PO | q12-24h | — | 🌎 NA |
| Susceptible infections (Chinchillas) | 50 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| Susceptible infections (Hamsters) | 20 mg/kg IM or SC q12h | IM/SC | q12h | — | 🌎 NA |
| Susceptible infections (Mice) | 25 mg/kg SC or IM q12h | SC/IM | q12h | — | 🌎 NA |
| Susceptible infections (Rats) | 6-10 mg/kg SC or IM q12h | SC/IM | q12h | — | 🌎 NA |
Birds
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Chlamydiosis (Small birds) | 0.05% concentration in food | PO | Continuous | — | 🌎 NA |
| Chlamydiosis (Larger psittacines) | 1% CTC concentration in food | PO | Continuous | — | 🌎 NA |
| Susceptible infections (Ratites) | 15-20 mg/kg PO three times daily | PO | TID | — | 🌎 NA |
| Susceptible infections (Pigeons) | 50 mg/kg PO q6-8h; or 1000-1500 mg/gallon drinking water | PO | q6-8h or continuous | — | 🌎 NA |
- Susceptible infections (Pigeons): In warm weather mix fresh every 12 hours. Calcium inhibits absorption; withhold grit and layer pellets during treatment.
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections | 6-10 mg/kg IV or IM; 10-20 mg/kg PO | IV/IM/PO | q24h | — | 🌎 NA |
- Susceptible infections: Generally administered once daily.
Swine
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections | 6-10 mg/kg IV or IM; 10-20 mg/kg PO | IV/IM/PO | q24h | — | 🌎 NA |
- Susceptible infections: Generally administered once daily.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Chlortetracycline is a broad-spectrum, first-generation tetracycline antibiotic. While it shares a nearly identical spectrum of activity with oxytetracycline and tetracycline, it is primarily utilized in veterinary medicine as a feed or water additive for food-producing animals (cattle, swine, poultry).
Key clinical features include:
- Broad-spectrum activity: Effective against many Mycoplasma, spirochetes (including Borrelia), Chlamydia, and Rickettsia.
- Increasing resistance: Many gram-positive and gram-negative bacteria (e.g., E. coli, Klebsiella, Pseudomonas) have developed resistance over time.
- Exotic animal use: Frequently used in avian medicine (especially for chlamydiosis) and in certain small mammals, though it is strictly contraindicated in guinea pigs due to fatal enterotoxemia.
Clinical Pearl: Because of its formulation as a feed/water additive, it is highly practical for herd or flock treatment, but individual dosing in companion animals is less common compared to newer tetracyclines like doxycycline.
Mechanism of action
Chlortetracycline is a bacteriostatic antibiotic that inhibits bacterial protein synthesis.
- Primary Mechanism: Reversibly binds to the 30S ribosomal subunit of susceptible organisms → blocks the binding of aminoacyl transfer-RNA to the mRNA-ribosome complex → halts peptide chain elongation.
- Secondary Mechanism: May also reversibly bind to 50S ribosomes and alter cytoplasmic membrane permeability.
- Mammalian effects: At very high concentrations, it can inhibit protein synthesis in mammalian cells, leading to antianabolic effects.
Safety & warnings
Contraindications
- Known hypersensitivity to chlortetracycline or other tetracyclines
- Guinea pigs (causes fatal clostridial enterotoxemia)
Adverse effects
- Gastrointestinal distress (nausea, vomiting, anorexia, diarrhea)
- Discoloration of developing teeth and bones (yellow, brown, or gray)
- Delayed bone growth and healing (at high doses)
- Hepatotoxicity
- Increased BUN (antianabolic effect)
- Ruminal microflora depression and stasis (in ruminants)
- Intravascular hemolysis and hemoglobinuria (with rapid IV injection of propylene glycol-based products)
- Colic, fever, and hair loss (in cats)
- Severe diarrhea (in stressed horses)
- Superinfections (bacterial or fungal overgrowth)
- Photosensitivity
Precautions
Pregnancy Warning: Tetracyclines can retard fetal skeletal development and discolor deciduous teeth. Use only in the last half of pregnancy if benefits outweigh risks.
Organ Impairment: Use with caution in patients with renal or hepatic insufficiency. Lower dosages and enhanced monitoring are recommended. Avoid concurrent use of other nephrotoxic or hepatotoxic drugs.
Laboratory Interactions:
- May cause falsely elevated urine catecholamines (fluorometric methods).
- May cause false-positive urine glucose (cupric sulfate method/Benedict's reagent) or false-negative urine glucose (glucose oxidase method).
IV Administration: Rapid IV injection can induce transient collapse and cardiac arrhythmias due to intravascular calcium chelation. Pre-treatment with IV calcium gluconate may be considered if rapid injection is unavoidable.
Drug interactions
Bacteriostatic action of tetracyclines may interfere with the bactericidal activity of penicillins and cephalosporins.
May interfere with bactericidal activity.
May increase the bioavailability of digoxin in a small percentage of patients, potentially leading to toxicity.
Chelation occurs, significantly decreasing the oral absorption of the tetracycline. Separate administration by at least 1-2 hours.
May depress plasma prothrombin activity; anticoagulant dosage may need adjustment.
Monitoring
- Clinical efficacy (resolution of infection)
- Gastrointestinal signs (vomiting, diarrhea, anorexia)
- Renal function (BUN, creatinine) and hepatic function, especially with prolonged use or in compromised patients
- Fluid and electrolyte status if severe GI distress occurs
Overdose
Tetracyclines are generally well tolerated after acute overdoses.
- Oral Overdose: Most likely associated with gastrointestinal disturbances (vomiting, anorexia, diarrhea). If severe emesis or diarrhea develops, monitor and replace fluids and electrolytes.
- Chronic Overdose: May lead to drug accumulation and nephrotoxicity.
- Ruminants: High oral doses can cause ruminal microflora depression and ruminoreticular stasis.
- Intravenous Overdose: Rapid IV injection of undiluted propylene glycol-based products can cause intravascular hemolysis and hemoglobinuria. Rapid IV injection can also induce transient collapse and cardiac arrhythmias due to chelation with intravascular calcium ions.
Available products
Formulations
- Feed additive
- Water mix preparation
- Soluble powder
Veterinary
- CTC®
- CLTC® 100 MR
- Aureomycin Sulmet® (with sulfamethazine)
- Aureo S 700® (with sulfamethazine)
- Aureomix 500® (with sulfamethazine and penicillin)
- Pennclor SP 250 & 500® (with sulfamethazine and penicillin)
- Aureozol 500® (with sulfathiazole and penicillin)
Regulatory status
Authorized for treatment of keratitis, conjunctivitis and blepharitis caused by susceptible bacteria.
POM-V classification
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store in tight containers and protect from light.
Client information
- Administration: If giving orally, do not administer at the same time as dairy products, antacids, or iron supplements, as these can bind to the drug and prevent it from working. Separate these by at least 1-2 hours.
- Side Effects: May cause stomach upset, vomiting, or diarrhea. If these signs become severe, contact your veterinarian.
- Young Animals: This medication can cause permanent yellow or brown staining of the teeth if given to young, growing animals or pregnant females.
- Sunlight: May make your pet's skin more sensitive to sunlight (photosensitivity). Avoid prolonged sun exposure during treatment.
- Birds: If treating birds via drinking water, mix fresh water every 12 hours in warm weather. Remove grit and layer pellets during treatment, as the calcium in them stops the drug from being absorbed.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.