Oxytetracycline (Ophthalmic)
Oxytetracycline hydrochloride
Also known as: Terramycin · Engemycin · Oxycare · Oxytetracycline/Polymyxin B · OTC
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 | 10 mg/kg | IM/SC | q24h | Not specified | 🌍 EU |
| Susceptible infections | 50 mg/kg loading dose, then 25 mg/kg | PO | q12h | up to 5 days | 🌍 EU |
- Susceptible infections: Give oral dose on an empty stomach.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Chlamydial/Mycoplasma keratoconjunctivitis | Apply 4 times daily | topical ophthalmic | q6h | 3-4 weeks | 🌎 NA |
| Susceptible infections (when no other agent is suitable) | 10 mg/kg | IM/SC | q24h | Not specified | 🌍 EU |
- Chlamydial/Mycoplasma keratoconjunctivitis: Dramatic improvement should be noted in 3-4 days, but treatment should continue for 3-4 weeks for Chlamydia to break the reproductive cycle. Better treatment is oral doxycycline 25 mg PO twice daily for three weeks.
- Susceptible infections (when no other agent is suitable): Only use in cats when no other agent is suitable.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Oxytetracycline is a broad-spectrum bacteriostatic antibiotic belonging to the tetracycline class.
- Veterinary Use: In veterinary ophthalmology, it is most frequently utilized in cats for the treatment of Chlamydia felis and Mycoplasma conjunctivitis, as well as for nonspecific or symptomatic therapy of undiagnosed conjunctivitis.
- Formulation: It is commercially available as an ophthalmic ointment in combination with Polymyxin B, which extends its spectrum to include many gram-negative organisms (such as Pseudomonas).
Clinical Pearl: While topical oxytetracycline is effective for managing clinical signs of chlamydial conjunctivitis, it often fails to clear the systemic carrier state. Systemic therapy (e.g., oral doxycycline) is generally preferred for complete clearance of the organism.
Mechanism of action
Oxytetracycline is a bacteriostatic antibiotic that inhibits bacterial protein synthesis.
- It reversibly binds to the 30S ribosomal subunit of susceptible organisms.
- This binding blocks the attachment of aminoacyl-tRNA to the mRNA-ribosome complex → inhibits the addition of amino acids to the growing peptide chain → halts bacterial growth and replication.
- The addition of Polymyxin B (in commercial ointments) disrupts the bacterial cell membrane of gram-negative bacteria, altering permeability and causing cell death.
Safety & warnings
Contraindications
- Known hypersensitivity to tetracyclines or polymyxin B
- Use of concentrated cattle/sheep depot formulations in small animals
- Pregnancy (last 2-3 weeks)
- Neonates (first month of life)
- Use in cats unless absolutely necessary
Adverse effects
- Local irritation
- Hypersensitivity reactions (rare)
- Potential for overgrowth of non-susceptible organisms (e.g., fungi) with prolonged use
- Vomiting
- Diarrhoea
- Depression
- Hepatotoxicity (rare)
- Fever
- Hypotension (following IV administration)
- Anorexia (especially in cats)
- Superinfections (with prolonged use)
- Renal tubular functional changes
- Teeth staining in developing animals
Precautions
Expect potential recurrence after discontinuation of topical treatment from organisms dormant in the nasal passage. Oral doxycycline is considered a better treatment to eliminate the carrier state of Chlamydia in cats.
Drug interactions
Bactericidal action of penicillins may be inhibited by oxytetracycline
Binds tetracycline, significantly reducing its GI absorption
Binds tetracycline, reducing its absorption
May increase the nephrotoxic effects
GI effects of tetracyclines may be increased
Monitoring
- Resolution of clinical signs (conjunctival hyperemia, chemosis, ocular discharge)
- Signs of local irritation or hypersensitivity
- Renal function (BUN, Creatinine, Urinalysis)
- Hydration status
- Gastrointestinal signs
Pharmacokinetics
Absorption
Minimal systemic absorption following topical ophthalmic application.
Distribution
Distributes locally into the tear film and superficial ocular tissues.
Metabolism
Undergoes enterohepatic recirculation.
Elimination
Excreted unchanged in urine and bile.
Overdose
Topical overdose is highly unlikely to cause systemic toxicity. If severe local irritation occurs, flush the eye with sterile saline and discontinue use.
Available products
Formulations
- Ophthalmic ointment (5 mg/g Oxytetracycline HCl with 10,000 Units/g Polymyxin B Sulfate)
- Injectable: 100 mg/ml solution
- Oral: 50 mg, 100 mg, 250 mg tablets
Veterinary
- Oxytetracycline HCl 5 mg/Polymyxin B Sulfate 10,000 Units/gm: 3.5 gram tubes; Terramycin® Ophthalmic Ointment
- Engemycin (100 mg/ml injectable)
- Oxycare (50 mg, 100 mg, 250 mg tablets)
Regulatory status
POM-V classification
POM-V classification
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store at controlled room temperature away from moisture and excessive heat. Keep tube tightly closed when not in use.
Client information
- Administration: Wash hands before and after application. Do not allow the tip of the tube to touch the eye, eyelids, or any other surface to prevent contamination.
- Duration: It is critical to continue treatment for the full 3-4 weeks as directed, even if the eye looks completely normal after a few days. Stopping early can lead to a relapse of the infection.
- Expectations: You should see dramatic improvement in your cat's eye within 3 to 4 days.
- Note: Your veterinarian may recommend an oral medication (like doxycycline) instead of or in addition to this ointment to fully clear the infection from your cat's system.
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.