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Tetracycline for Veterinary Use

by Barbara Forney, VMD

Basic Information

Tetracycline is a broad-spectrum antibiotic from the same family as oxytetracycline, doxycycline, minocycline, and others. The tetracycline antibiotics are bacteriostatic. Their mechanism of action is through the reversible binding of bacterial 30S ribosomes and the alteration of the bacterial cytoplasmic membrane. Tetracycline antibiotics are used to treat bacterial infections due to aerobic, gram-positive and gram-negative bacteria, mycoplasma, rickettsiae, chlamydia, and some protozoa. Doxycycline and minocycline have greater lipid solubility than tetracycline and may be more effective against some Staphylococcal infections. Certain gram-negative bacteria, particularly Pseudomonas and some enteric bacteria, are resistant to tetracycline.

Tetracycline is well-absorbed after oral administration, although the presence of food, and particularly dairy products, will reduce oral absorption. Tetracycline is excreted through the kidneys and the gastrointestinal (GI) tract. Tetracycline antibiotics are widely distributed throughout the body, although therapeutic levels may not be reached in the central nervous system. Doxycycline and minocycline may reach higher levels in some of the ore difficult to penetrate tissues such as the prostate and eye.

Dogs and Cats

Oral tetracycline is used in dogs and cats to treat susceptible bacterial infections and infections due to other susceptible organisms. Tetracycline has some immunomodulatory properties and may be used with steroids and niacinamide to treat cutaneous discoid lupus erythematosus of dogs. When used to treat autoimmune disease, there may be a considerable lag (one to two months) before appreciable improvement is seen.

Ophthalmic tetracycline is used to treat Chlamydial, Mycoplasma, and non-specific conjunctivitis in the cat. Although topical ophthalmic tetracycline is useful for improving the clinical signs associated with Chlamydia, systemic treatment with doxycycline may be necessary to eliminate the organism.

Side Effects

  • Side effects due to oral tetracycline use are generally related to GI tract. These include nausea, anorexia, vomiting, and diarrhea.
  • Cats may not tolerate oral tetracycline as well as dogs. Cats may also develop fever, abdominal pain, hair loss, and depression.
  • Systemic use of tetracycline antibiotics may be associated with increased photosensitivity and, rarely, with urolith formation, blood dyscrasias, and hepatotoxicity.


  • Tetracycline is generally not used in pregnant or lactating animals due to effects on bone development and discoloration of teeth. It may also cause tooth discoloration when used in very young animals. Doxycycline or minocycline are frequently substituted for tetracycline in these populations.
  • Tetracycline should be used with caution and at a lower dose in animals with decreased renal or hepatic function. Tetracycline should not be used concurrently with other drugs that are potentially hepato- or nephro-toxic.

Drug Interactions

  • Tetracycline antibiotics are generally not combined with bactericidal antibiotics such as aminoglycosides, penicillin, and cephalosporins.
  • Oral Tetracycline antibiotic should not be given at the same time as oral antacids or any oral GI product containing bismuth, calcium, zinc, aluminum, magnesium, or iron. If it is necessary to use these products concurrently, they should be separated by one to two hours.
  • Patients receiving either digoxin or anticoagulant therapy may need additional monitoring and possible dosage-adjustment. Tetracycline may decrease atovaquone levels.
  • Tetracyline should not be used with methoxyflurane due to potential nephrotoxicity.


  • Acute oral overdose with tetracycline may cause gastro-intestinal disturbances similar to those described under side effects. In cases with severe vomiting or diarrhea, intravenous fluids and monitoring of electrolytes may be necessary.
  • Chronic overdose with tetracycline may cause nephrotoxicity.
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Therapeutic Class

Dogs and Cats

May Be Prescribed by Vets for:
Susceptible infections

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About the Author

Dr. Barbara Forney

Barbara Forney, VMD

Dr. Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania. She has a master's degree in animal science from the University of Delaware and graduated from the University of Pennsylvania School of Veterinary Medicine in 1982.

She began to develop her interest in client education and medical writing in 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.

Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.