Oxytetracycline

Tetracycline Antibiotic Polyketide Antibiotics

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 15-25 mg/kg q8h Duration: 5-7 days or as directed
Notes: Administer on an empty stomach, 1 hour before or 2 hours after feeding. Avoid concurrent administration with dairy products, antacids, or iron supplements.
Dog IV 5-10 mg/kg q12h Duration: As directed
Notes: Administer slowly over 5 minutes. Not for IM or SC in dogs due to pain and tissue irritation.
Cat PO 15-25 mg/kg q8h Duration: 5-7 days or as directed
Notes: Administer on an empty stomach. Avoid concurrent administration with dairy products, antacids, or iron supplements.
Cat IV 5-10 mg/kg q12h Duration: As directed
Notes: Administer slowly over 5 minutes. Not for IM or SC in cats due to pain and tissue irritation.
Horse IV 5-10 mg/kg q12h Duration: As directed
Notes: Administer slowly over 5 minutes. Not for IM due to severe tissue irritation.
Horse PO 10-20 mg/kg q12h Duration: As directed
Notes: Oral absorption is variable; use with caution. Administer on an empty stomach.
Cattle IM 10-20 mg/kg q24h Duration: 3-5 days
Notes: Use long-acting formulation (LA) for single-dose therapy. Administer in the neck to minimize tissue damage. Observe withdrawal times.
Cattle IV 5-10 mg/kg q12h Duration: As directed
Notes: Administer slowly. Not for IM in lactating dairy cattle due to milk residues.
Sheep/Goat IM 10-20 mg/kg q24h Duration: 3-5 days
Notes: Use long-acting formulation if available. Administer in the neck. Observe withdrawal times.
Rabbit PO 20-50 mg/kg q8-12h Duration: 5-7 days
Notes: May cause GI disturbances; monitor for diarrhea. Administer with water or small amount of food if tolerated.
Poultry PO (drinking water) 10-20 mg/kg body weight per day q24h Duration: 3-5 days
Notes: Prepare fresh solution daily. Ensure adequate water intake. Observe withdrawal times for eggs and meat.
Reptiles IM 10-20 mg/kg q24-48h Duration: As directed
Notes: Use caution in dehydrated animals. May cause tissue irritation at injection site.

Clinical Indications & Species Uses

General Indications
  • Treatment of bacterial infections caused by susceptible gram-positive and gram-negative organisms, Mycoplasma, Rickettsia, Chlamydia, and some protozoa.
Dog (Canine)
  • Treatment of bacterial infections caused by susceptible organisms, including respiratory tract infections, urinary tract infections, skin infections, and soft tissue infections.
  • Treatment of rickettsial diseases such as Rocky Mountain spotted fever and ehrlichiosis.
  • Treatment of leptospirosis.
  • Treatment of brucellosis (in combination with other antibiotics).
  • Treatment of Bordetella bronchiseptica infections (kennel cough).
Cat (Feline)
  • Treatment of bacterial infections caused by susceptible organisms, including respiratory tract infections, urinary tract infections, and skin infections.
  • Treatment of rickettsial diseases such as hemobartonellosis (Mycoplasma haemofelis).
  • Treatment of Chlamydophila felis conjunctivitis.
  • Treatment of Bordetella bronchiseptica infections.
Horse (Equine)
  • Treatment of respiratory tract infections, including pneumonia and pleuropneumonia.
  • Treatment of bacterial infections caused by susceptible organisms, including wounds and abscesses.
  • Treatment of Potomac horse fever (Neorickettsia risticii).
  • Treatment of Lyme disease (Borrelia burgdorferi).
Cattle (Bovine)
  • Treatment of respiratory disease complex (shipping fever, pneumonia) caused by Pasteurella, Mannheimia, and Mycoplasma.
  • Treatment of foot rot (interdigital necrobacillosis).
  • Treatment of metritis and other reproductive tract infections.
  • Treatment of leptospirosis.
  • Treatment of anaplasmosis.
Small Ruminants (Sheep / Goat)
  • Treatment of respiratory tract infections (pneumonia).
  • Treatment of foot rot.
  • Treatment of enteric infections.
  • Treatment of chlamydial infections (e.g., enzootic abortion).
Rabbit & Small Mammals
  • Treatment of respiratory tract infections (e.g., Pasteurella multocida).
  • Treatment of enteric infections (e.g., Clostridium spiroforme).
Avian & Poultry
  • Treatment of respiratory infections (e.g., Mycoplasma gallisepticum, Ornithobacterium rhinotracheale).
  • Treatment of colibacillosis (E. coli).
  • Treatment of fowl cholera (Pasteurella multocida).
Exotic & Other Species
  • Treatment of bacterial infections in reptiles (e.g., respiratory infections, shell rot).
  • Treatment of bacterial infections in small mammals (e.g., guinea pigs, hamsters).
  • Treatment of bacterial infections in fish (e.g., furunculosis, columnaris).

Pharmacology & Mechanism of Action

Drug Class: Tetracycline Antibiotic | Pharmacological Group: Polyketide Antibiotics

Mechanism of Action: Oxytetracycline inhibits bacterial protein synthesis by binding reversibly to the 30S ribosomal subunit, specifically to the 16S rRNA, preventing the attachment of aminoacyl-tRNA to the mRNA-ribosome complex. This blocks the addition of new amino acids to the growing peptide chain, thereby inhibiting bacterial growth. It is generally bacteriostatic, but may be bactericidal at high concentrations. It is effective against a wide range of gram-positive and gram-negative bacteria, as well as Mycoplasma, Rickettsia, Chlamydia, and some protozoa.

Pharmacodynamics: Oxytetracycline exhibits time-dependent antibacterial activity, with the primary pharmacodynamic index being the time above the minimum inhibitory concentration (T > MIC). It has a broad spectrum of activity, but resistance can develop via efflux pumps, ribosomal protection proteins, or enzymatic inactivation. It is often used for its activity against Mycoplasma and intracellular pathogens. In veterinary medicine, it is commonly used for respiratory, enteric, and systemic infections.

⚡ Pharmacokinetics Summary

Absorption: Oxytetracycline is well absorbed after oral administration in monogastric animals, but absorption is reduced in ruminants due to ruminal degradation and binding to feed. It is also absorbed after intramuscular and subcutaneous administration, with peak plasma concentrations achieved within 1-2 hours for parenteral routes. Oral absorption is enhanced on an empty stomach, but food and divalent cations (calcium, magnesium, iron) can chelate and reduce absorption.
Distribution: Oxytetracycline is widely distributed throughout the body, including into tissues and body fluids such as pleural, peritoneal, and synovial fluids. It crosses the placenta and is excreted in milk. It has a volume of distribution of approximately 1-2 L/kg in most species. It accumulates in the reticuloendothelial system, liver, spleen, and bone, where it can chelate calcium.
Metabolism: Oxytetracycline is minimally metabolized in the liver. The majority of the drug is excreted unchanged in the urine and feces. In ruminants, some metabolism by ruminal microflora may occur.
Excretion: Excretion occurs primarily via the kidneys through glomerular filtration, with a smaller portion excreted in bile and feces. In animals with renal impairment, the half-life may be prolonged, requiring dose adjustment.
Half-Life: Dogs: approximately 6-8 hours; Cats: approximately 6-8 hours; Horses: approximately 10-12 hours; Cattle: approximately 9-12 hours; Sheep/Goats: approximately 4-6 hours; Pigs: approximately 6-8 hours; Poultry: approximately 5-10 hours.
Bioavailability: Oral bioavailability is variable: dogs and cats ~60-80% on an empty stomach; ruminants <30% due to ruminal degradation; parenteral (IM/SC) bioavailability is nearly 100%.
Protein Binding: Oxytetracycline is approximately 20-40% bound to plasma proteins, depending on the species.

Available Formulations & Strengths

Oral Tablet 100 mg, 250 mg, 500 mg (PO)
Oral Capsule 100 mg, 250 mg (PO)
Oral Solution 100 mg/mL (PO)
Injectable Solution 50 mg/mL, 100 mg/mL, 200 mg/mL (long-acting) (IV, IM, SC)
Powder for Oral Solution Various (e.g., 100 g per 100 g powder) (PO (drinking water))
Ophthalmic Ointment 1% (Ophthalmic)
Ophthalmic Solution 0.5% (Ophthalmic)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to tetracyclines
  • Severe hepatic or renal impairment (use with caution)
  • Pregnancy (especially in the last trimester) due to potential effects on fetal bone and teeth development
  • Young animals (during tooth development) due to risk of tooth discoloration and enamel hypoplasia
  • Concurrent use with other bacteriostatic antibiotics that may antagonize bactericidal antibiotics
  • Oral administration in ruminants with functional rumen (may disrupt ruminal flora and reduce efficacy)
Warnings & Clinical Precautions:
  • Use with caution in animals with renal or hepatic impairment; adjust dose or extend dosing interval.
  • Avoid use in pregnant animals unless the benefits outweigh risks; tetracyclines can cross the placenta and cause fetal skeletal and dental abnormalities.
  • Avoid use in young animals (less than 6 months of age for dogs and cats, less than 2 years for horses) due to tooth discoloration and bone growth retardation.
  • Intramuscular injection can cause severe tissue irritation and pain; use the IV route when possible in small animals and horses.
  • In ruminants, oral administration may disrupt ruminal microflora; use parenteral routes when possible.
  • May cause photosensitivity; avoid excessive sunlight exposure during treatment.
  • Use in animals with myasthenia gravis may exacerbate neuromuscular blockade.
  • Do not use in animals with a history of allergy to tetracyclines.
  • In food animals, observe withdrawal times to avoid drug residues in meat and milk.

Adverse Effects & Reactions

Common:

  • Gastrointestinal upset (nausea, vomiting, diarrhea)
  • Tooth discoloration in young animals
  • Injection site reactions (pain, swelling, tissue necrosis) with IM administration
  • Photosensitivity (skin reactions on exposure to sunlight)

Serious / Severe:

  • Hepatotoxicity (especially with high doses or prolonged use)
  • Nephrotoxicity (especially in animals with pre-existing renal disease)
  • Esophageal ulceration or stricture (if oral tablets lodge in esophagus)
  • Superinfection with resistant organisms (e.g., Candida, Clostridium difficile)
  • Blood dyscrasias (rare)
  • Anaphylaxis (rare)

Rare:

  • Blood dyscrasias (leukopenia, thrombocytopenia)
  • Pseudotumor cerebri (intracranial hypertension)
  • Pancreatitis
  • Allergic reactions (urticaria, angioedema)
  • Crystalluria

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Antacids containing aluminum, calcium, magnesium, or bismuth Reduced absorption of oxytetracycline due to chelation; separate administration by at least 2 hours. High
Iron supplements, zinc, or dairy products Reduced absorption of oxytetracycline due to chelation; separate administration by at least 2 hours. High
Bactericidal antibiotics (e.g., penicillins, cephalosporins) Potential antagonism; avoid concurrent use. Moderate
Oral contraceptives (in humans, but relevant in animals for research) Reduced efficacy of oral contraceptives; not commonly relevant in veterinary medicine. Mild
Warfarin and other anticoagulants Enhanced anticoagulant effect; monitor coagulation parameters. Moderate
Methoxyflurane (anesthetic) Increased risk of nephrotoxicity; avoid concurrent use. High
Digoxin Increased digoxin bioavailability due to alteration of gut flora; monitor digoxin levels. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Gastrointestinal signs (vomiting, diarrhea, anorexia)
  • Hepatotoxicity (elevated liver enzymes, jaundice)
  • Nephrotoxicity (increased BUN/creatinine, renal failure)
  • Neurological signs (ataxia, depression) in severe cases
  • Tooth discoloration and enamel hypoplasia in young animals

Emergency Treatment Protocol: Treatment is primarily supportive. Discontinue the drug immediately. Induce vomiting if recent oral ingestion and the animal is conscious. Administer activated charcoal to reduce absorption. Provide intravenous fluids to maintain hydration and promote renal excretion. Monitor liver and kidney function. In severe cases, consider hemodialysis or peritoneal dialysis. There is no specific antidote.

Food Animal Withdrawal Times

🥩 Meat: 28 days🥛 Milk: 7 days🥚 Eggs: 7 days

Withdrawal times vary by formulation (short-acting vs. long-acting) and country. Always follow label instructions and local regulations. For long-acting formulations, meat withdrawal may be up to 35 days. In poultry, egg withdrawal is typically 7 days. In cattle, milk withdrawal is typically 7 days for short-acting and 14 days for long-acting.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F), with excursions permitted between 15-30°C (59-86°F).

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light and moisture. Keep container tightly closed. Do not freeze injectable solutions. Store oral powders in a dry place.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: FDA-approved for use in cattle, swine, sheep, and poultry for various indications. Also approved for dogs and cats for certain infections. Many formulations are available as generic.

Extra-Label (Off-Label) Use: In the United States, extra-label use of oxytetracycline in food animals is permitted under AMDUCA (Animal Medicinal Drug Use Clarification Act) only with a valid veterinary-client-patient relationship and a written prescription. Extra-label use in non-food animals is allowed. However, extra-label use in feed is prohibited. In the EU, similar regulations apply under Directive 2001/82/EC.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Oxytetracycline is a broad-spectrum antibiotic commonly used in veterinary practice for a variety of infections. It is particularly valuable for treating Mycoplasma and Rickettsial infections. Due to its chelation properties, oral absorption is significantly reduced when administered with food, dairy products, or supplements containing divalent cations. Therefore, it should be given on an empty stomach. Parenteral administration is often preferred in ruminants due to poor oral bioavailability. Long-acting formulations provide sustained plasma concentrations and are convenient for single-dose therapy in cattle. However, they can cause severe injection site reactions; therefore, subcutaneous administration is recommended in cattle to minimize tissue damage. In small animals, IV administration is preferred to avoid pain and tissue necrosis associated with IM injections. Oxytetracycline should be used judiciously to minimize the development of antimicrobial resistance. In food animals, strict adherence to withdrawal times is essential to prevent drug residues in meat, milk, and eggs. Monitoring for adverse effects, particularly gastrointestinal upset and hepatotoxicity, is recommended during therapy.

References & Literature

  • 📚 Plumb's Veterinary Drug Handbook
  • 📚 Papich Veterinary Pharmacology and Therapeutics
  • 📚 Compendium of Veterinary Products (CVP)