Tetracycline
Tetracycline hydrochloride
Also known as: Aquadrops · Panmycin · Sumycin · Polyotic · Delta Albaplex · Tetracycline HCl · tetracyclini hydrochloridum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Audited v13 dosing evidence
Structured calculator evidenceSusceptible infections (extra-label)
- q8-12h
NA
Governing clinical context (2)
- ■ This medicine is best given without food. Avoid giving this medicine orally within 1 to 2 hours of milk or other dairy products.
- Unless otherwise instructed by the manufacturer, tetracycline oral tablets and capsules should be stored in tight, light-resistant containers at room temperature (15°C-30°C [59°F-86°F]).
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Tetracycline is a prototype, short-acting tetracycline antibiotic. While historically used as a broad-spectrum antimicrobial, increasing bacterial resistance has shifted its clinical role.
In modern veterinary medicine:
- Small Animal Practice: Doxycycline is generally preferred for infectious diseases due to better tissue penetration and dosing frequency. However, tetracycline is frequently used in combination with niacinamide for its immunomodulatory effects to treat immune-mediated skin conditions (e.g., discoid lupus erythematosus, pemphigus).
- Large Animal Practice: Oxytetracycline is typically preferred over tetracycline.
Clinical Pearls:
- It remains effective against atypical organisms like Mycoplasma, Rickettsia, spirochetes (e.g., Lyme disease), and Chlamydia.
- It possesses significant anti-inflammatory and immunomodulating properties, making it valuable in veterinary dermatology.
Mechanism of action
Tetracycline is a time-dependent, bacteriostatic antibiotic.
- Antimicrobial Action: Reversibly binds to the 30S ribosomal subunit of susceptible organisms → prevents binding of aminoacyl transfer-RNA to the ribosome → inhibits bacterial protein synthesis. It may also bind to the 50S subunit and alter cytoplasmic membrane permeability.
- Immunomodulatory/Anti-inflammatory Action: Suppresses antibody production and neutrophil chemotaxis. Inhibits key inflammatory mediators including lipases, collagenases, prostaglandin synthesis, and the activation of complement component 3.
Safety & warnings
Contraindications
- Hypersensitivity to tetracyclines
- Pregnancy (last half) - retards fetal skeletal development and discolors teeth
- Young, growing animals (unless benefits outweigh risks)
Adverse effects
- Gastrointestinal distress (nausea, vomiting, anorexia, diarrhea)
- Discoloration of developing teeth and bones (yellow/brown/gray)
- Delayed bone growth and healing in young animals
- Superinfections (bacterial or fungal overgrowth)
- Photosensitivity
- Urolith formation (with long-term use in dogs)
- Hepatotoxicity and blood dyscrasias (rare)
- Cats: Colic, fever, hair loss, depression (poorly tolerated)
- Horses: Severe diarrhea (especially if stressed)
- Ruminants: Ruminal microflora depression and stasis (high oral doses)
- Injection site reactions (IM): Local necrosis and yellow staining
Precautions
Extreme Caution: Pregnancy (Category D). Can cause congenital malformations, embryotoxicity, and discoloration of deciduous teeth.
- Renal/Hepatic Impairment: Use cautiously. Lower dosages and enhanced monitoring are recommended. Avoid concurrent nephrotoxic or hepatotoxic drugs.
- Cats: Do not tolerate oral tetracycline well; monitor closely for adverse effects.
- IV Administration: Rapid IV injection can cause transient collapse and cardiac arrhythmias due to calcium chelation. Administer slowly or pre-treat with IV calcium gluconate if rapid injection is necessary.
Drug interactions
Tetracyclines may decrease atovaquone levels.
Theoretical antagonism of bactericidal activity, though clinical significance is doubtful.
May increase bioavailability of digoxin, potentially causing toxicity that persists for months.
Chelation occurs, significantly decreasing the absorption of tetracycline. Separate doses by at least 1-2 hours.
Concomitant use can cause fatal nephrotoxicity.
May impair oral absorption of tetracycline; separate dosing by at least 2 hours.
May depress plasma prothrombin activity; anticoagulant dosage adjustment may be needed.
Monitoring
- Adverse effects (GI signs, injection site reactions)
- Clinical efficacy
- Periodic renal, hepatic, and hematologic evaluations (with long-term use or in susceptible patients)
Pharmacokinetics
Half-life
Absorption
Readily absorbed after oral administration in fasting animals (bioavailability ~60-80%). Food or dairy products can significantly reduce absorption by 50% or more. Erratically and poorly absorbed after IM administration.
Distribution
Widely distributed to heart, kidney, lungs, muscle, pleural fluid, bronchial secretions, bile, saliva, urine, synovial fluid, and aqueous/vitreous humor. Poor penetration into CSF. Crosses the placenta and distributes into milk. Volume of distribution is ~1.2-1.3 L/kg in small animals and 1-2.5 L/kg in cattle.
Metabolism
Apparently not metabolized.
Elimination
Eliminated unchanged primarily via glomerular filtration. Excreted into the GI tract via biliary and nonbiliary routes (may become inactive after chelation with fecal materials). Patients with impaired renal function can accumulate the drug.
Overdose
Tetracyclines are generally well tolerated after acute overdoses.
- Oral Overdose: Most likely associated with GI disturbances (vomiting, anorexia, diarrhea). Monitor fluids and electrolytes if severe emesis/diarrhea occurs.
- Chronic Overdose: May lead to drug accumulation and nephrotoxicity.
- Ruminants: High oral doses can cause ruminal microflora depression and ruminoreticular stasis.
- IV Overdose/Rapid Injection: Rapid IV injection can induce transient collapse and cardiac arrhythmias, presumably due to chelation with intravascular calcium ions. If rapid IV administration is necessary, pre-treatment with intravenous calcium gluconate is recommended by some clinicians.
Available products
Formulations
- Capsules
- Oral Suspension
- Soluble Powder (water additive)
- Injection (rarely used in small animals)
Veterinary
- Tetracycline HCl Soluble Powder (water additive): 25 grams/lb or 324 grams/lb
- Delta Albaplex (Combination product containing tetracycline, novobiocin, and prednisone)
Human-labeled
- Tetracycline HCl Capsules: 250 mg & 500 mg (Sumycin, generic)
- Tetracycline HCl Oral Suspension: 25 mg/mL (Sumycin Syrup)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store oral tablets and capsules in tight, light-resistant containers at room temperature (15-30°C). Store oral suspension and powder for injection at room temperature; avoid freezing the oral suspension.
Client information
- Administration: Give this medication on an empty stomach if possible. Avoid giving within 1-2 hours of feeding, or giving milk/dairy products, as these can significantly decrease drug absorption.
- GI Upset: If your pet vomits or acts nauseated, giving the medication with a small amount of non-dairy food may help, though it may reduce the drug's effectiveness slightly.
- Sunlight: This medication may make your pet's skin more sensitive to sunlight (photosensitivity). Avoid prolonged sun exposure.
- Discoloration: Be aware that in young, growing animals, this drug can cause permanent yellow or brown staining of the teeth.
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.