Doxycycline
Doxycycline calcium, Doxycycline hyclate, Doxycycline monohydrate
Also known as: Vibramycin · Doxirobe · Periostat · Doryx · Oracea · Monodox · Adoxa · Atridox · Doxybactin · Ronaxan · Doxycycline hydrochloride · Doxycycline monohydrate · Doxycyclinum · GS-3065 · Doxycycline hyclate
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Audited v13 dosing evidence
Structured calculator evidenceBorreliosis (ie, Borrelia burgdorferi [Lyme disease]) (extra-label)
- q12-24h
NA
Governing clinical context (2)
- ■ Do not give multivitamins, calcium supplements, antacids, or laxatives 2 hours before or after giving doxycycline as these products can reduce effectiveness of the medicine.
- Doxycycline hyclate tablets and capsules should be stored in tight, light-resistant containers below 30°C (86°F), preferably at controlled room temperature (15°C to 30°C [59°F-86°F]). After being reconstituted with water, the monohydrate oral suspension is stable for 14 days when stored at room temperature.
Susceptible bacterial infections (extra-label)
- q12-24h
NA
Governing clinical context (2)
- ■ Do not give multivitamins, calcium supplements, antacids, or laxatives 2 hours before or after giving doxycycline as these products can reduce effectiveness of the medicine.
- Doxycycline hyclate tablets and capsules should be stored in tight, light-resistant containers below 30°C (86°F), preferably at controlled room temperature (15°C to 30°C [59°F-86°F]). After being reconstituted with water, the monohydrate oral suspension is stable for 14 days when stored at room temperature.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Doxycycline is a broad-spectrum, semi-synthetic tetracycline antibiotic derived from oxytetracycline. It is widely used in veterinary medicine due to its favorable pharmacokinetic profile compared to older tetracyclines.
Key Clinical Advantages:
- High Lipophilicity: Penetrates tissues exceptionally well, including the central nervous system (CSF), prostate, and eye.
- Renal Safety: Unlike other tetracyclines, doxycycline is primarily excreted in the feces as an inactive chelate. It does not accumulate in patients with renal dysfunction, making it the tetracycline of choice for azotemic patients.
- Heartworm Adjunct: Doxycycline is a critical component of modern canine heartworm (Dirofilaria immitis) treatment protocols. It eliminates Wolbachia, an endosymbiotic bacterium essential for heartworm survival and reproduction, thereby weakening the adult worms and reducing post-adulticide pulmonary pathology.
It is highly effective against atypical organisms including Borrelia (Lyme disease), Leptospira, Rickettsiae, Chlamydia, Mycoplasma, Bartonella, and Bordetella.
Mechanism of action
Doxycycline is a bacteriostatic antibiotic.
- Primary Mechanism: It reversibly binds to the 30S ribosomal subunit of susceptible organisms → prevents the binding of aminoacyl transfer-RNA to the mRNA-ribosome complex → inhibits bacterial protein synthesis.
- Secondary Mechanisms: It may also reversibly bind to 50S ribosomes and alter cytoplasmic membrane permeability.
- Anti-inflammatory/Immunomodulatory Effects: Beyond its antimicrobial properties, doxycycline inhibits matrix metalloproteinases (MMPs) and scavenges reactive oxygen species, which contributes to its efficacy in treating chronic inflammatory conditions (e.g., idiopathic rhinitis, arthritis).
Safety & warnings
Contraindications
- Hypersensitivity to tetracyclines
- Intravenous administration in horses (associated with fatal cardiac arrhythmias)
- First half of pregnancy (can retard fetal skeletal development and discolor deciduous teeth, though less likely than other tetracyclines)
- Pregnant animals
- Animals with evidence of oesophagitis or dysphagia
Adverse effects
- Vomiting
- Diarrhea
- Anorexia
- Elevated liver enzymes (ALT, ALP)
- Esophageal strictures (especially in cats if dry-pilled)
- Superinfections (non-susceptible bacteria or fungi)
- Photosensitivity (reported in humans)
- Cardiac arrhythmias, collapse, and death (if given IV to horses)
- Nausea
- Diarrhoea
- Oesophagitis
- Oesophageal ulceration/stricture (especially in cats)
- Tooth discoloration (if given during tooth development, though risk is lower than other tetracyclines)
Precautions
WARNING: Do not administer IV to horses due to risk of fatal cardiac arrhythmias. Do not give IM or SC to any species.
- Esophageal Strictures: Highly associated with "dry pilling" in cats. Always follow oral solid doses with at least 6 mL of water or liquid.
- Hepatotoxicity: Use with caution in animals with significant liver dysfunction, as increases in hepatic enzymes have been documented.
- Pregnancy/Pediatric: Use with caution in pregnant and young animals due to potential for bone and teeth abnormalities, though doxycycline is safer than older tetracyclines.
- MDR1 Mutants: Safe to use; no dose alterations recommended for dogs with MDR1 mutations.
Drug interactions
Chelates with divalent/trivalent cations, significantly decreasing doxycycline absorption. Give at least 1-2 hours apart.
May reduce gastrointestinal absorption of doxycycline.
Decreases tetracycline absorption. Give iron 3 hours before or 2 hours after doxycycline.
Bacteriostatic drugs (doxycycline) may theoretically interfere with the bactericidal activity of these antibiotics.
May decrease doxycycline half-life and reduce serum levels.
Tetracyclines may depress plasma prothrombin activity; anticoagulant dosage may need adjustment.
Reduced absorption of doxycycline
Reduced absorption of doxycycline
Reduced absorption of doxycycline
Reduced absorption of doxycycline
May increase doxycycline metabolism, decreasing plasma levels
Reduced absorption of doxycycline (though less marked than with water-soluble tetracyclines)
Monitoring
- Clinical efficacy
- Adverse effects (GI upset)
- Liver enzymes (ALT, ALP) with prolonged use
- Clinical response to therapy
- Signs of dysphagia, regurgitation, or oesophagitis (especially in cats)
- Gastrointestinal upset
Pharmacokinetics
Half-life
Absorption
Well absorbed after oral administration (90-100% bioavailability in humans/monogastrics). Unlike other tetracyclines, absorption is only minimally reduced (by ~20%) by food or dairy products. However, in horses, feeding can reduce bioavailability to <5% due to high fiber content.
Distribution
Highly lipid-soluble. Widely distributed to heart, kidney, lungs, muscle, pleural fluid, bronchial secretions, bile, saliva, synovial fluid, and aqueous/vitreous humor. Penetrates CSF, prostate, and eye better than other tetracyclines. Volume of distribution (Vd) in dogs is ~1.5 L/kg. Protein binding: 75-86% (dogs), 82% (horses), 93% (cattle/pigs/cats).
Metabolism
Partially inactivated in the intestine by chelate formation.
Elimination
Primarily excreted into the feces via non-biliary routes in an inactive form (chelate). Renal excretion accounts for only ~25% in dogs, and biliary excretion <5%. Does not accumulate in patients with renal dysfunction.
Overdose
Doxycycline is generally quite safe in mild overdose situations (except for IV administration in horses).
- Oral Overdose: Most likely associated with gastrointestinal disturbances (vomiting, anorexia, diarrhea).
- Treatment: Oral administration of divalent or trivalent cation antacids (e.g., calcium, magnesium, aluminum) can bind the drug in the gut and reduce GI distress. Monitor and replace fluids/electrolytes if severe emesis or diarrhea occurs.
- IV Overdose: Rapid intravenous injection has induced transient collapse and cardiac arrhythmias in several species, presumably due to chelation with intravascular calcium ions.
Available products
Formulations
- Delayed-Release Tablets and Capsules
- Powder for Oral Suspension
- Oral Syrup
- Injection (Lyophilized powder)
- Periodontal Gel (8.5%)
- 20 mg tablet
- 50 mg tablet
- 100 mg tablet
- 200 mg tablet
- 400 mg tablet
- Oral paste (named patient basis)
Veterinary
- Doxirobe® (Pfizer): Doxycycline gel 8.5% activity once mixed (for periodontal disease in dogs)
- Doxybactin 20 mg, 50 mg, 200 mg, 400 mg tablets
- Ronaxan 20 mg, 100 mg tablets
- Oral paste (named patient basis)
Human-labeled
- Periostat®, Alodox Convenience Kit®, Vibramycin®, Vibra-Tabs®, Oraxyl®, generic: Tablets & Capsules (20 mg, 50 mg, 100 mg)
- Doryx®, Oracea®: Delayed-Release Tablets & Capsules (40 mg, 75 mg, 100 mg, 150 mg)
- Monodox®, Adoxa®, generic: Tablets and Capsules (as monohydrate) (50 mg, 75 mg, 100 mg, 150 mg)
- Vibramycin®, Doxycycline (Teva): Powder for Oral Suspension (5 mg/mL after reconstitution)
- Vibramycin®: Oral Syrup (as calcium salt) (10 mg/mL)
- Atridox®: Injection (42.5 mg in vials)
- Doxy®-100 & -200, generic: Lyophilized Powder for Injection (100 mg, 200 mg)
Regulatory status
POM-V
POM-V
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Tablets and capsules should be stored in tight, light-resistant containers at <30°C (preferably 15-30°C). Reconstituted monohydrate oral suspension is stable for 14 days at room temperature. Compounded oral suspensions degrade rapidly between 7-14 days even if refrigerated. Tablets mixed with water/food lose >10% potency after 24 hours. Reconstituted hyclate injection (0.1-1 mg/mL) is stable for 72 hours refrigerated.
Client information
- CRITICAL WARNING FOR CATS: Do not "dry pill" your pet. Doxycycline capsules or tablets can stick in the esophagus and cause severe, permanent damage (strictures). Always follow the pill with at least 6 mL (a little more than a teaspoon) of water or liquid. Buttering the lips after administration can induce salivation and help the pill go down.
- Food and Dairy: Doxycycline can be given with or without food. Giving it with food may help prevent stomach upset. Unlike older tetracyclines, milk or dairy products do not significantly block the absorption of doxycycline.
- Sunlight: In rare cases, this medication can make skin more sensitive to sunlight.
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.