Doxycycline

Doxycycline is a tetracycline antibacterial with useful tissue and intracellular penetration. It is widely used for vector-borne bacterial diseases, feline hemoplasmosis and selected respiratory infections. A distinct role in canine heartworm treatment is reduction of Wolbachia, the bacterial endosymbiont associated with Dirofilaria immitis, as part of a broader parasite-treatment protocol.

Group

Tetracycline antibacterial

Mechanism of Action

Doxycycline reversibly binds the bacterial 30S ribosomal subunit and prevents aminoacyl-transfer RNA from accessing the acceptor site. This interrupts peptide-chain elongation and protein synthesis, usually producing bacteriostatic activity. Intracellular distribution supports treatment of susceptible rickettsial and related pathogens. Suppression of Wolbachia impairs bacterial support of heartworms and can reduce inflammatory consequences associated with parasite death.

Dose Rates

Dog

Use / stage	Dose	Route	Schedule	Instructions
Bacterial infection	5 mg/kg	PO, IV	Every 12 h
Bacterial infection	10 mg/kg	PO	Every 24 h
Rickettsial infection	5 mg/kg	PO	Every 12 h
Ehrlichiosis	5 mg/kg	PO	Every 12 h	At least 14 days; studies describe 3–4-week courses.
Heartworm adjunct	10 mg/kg	PO	Every 12 h	Up to 28 days; Wolbachia-directed course before adulticide treatment, within the complete heartworm protocol.
Toxoplasmosis	5–10 mg/kg	PO	Every 12 h	Up to 28 days
Granulocytic anaplasmosis	5 mg/kg	PO	Every 12 h	Up to 14 days
Salmon poisoning disease	10 mg/kg	IV	Every 12 h	At least seven days; Neorickettsia helminthoeca.
Antiarthritic adjunct	3–4 mg/kg	PO	Every 24 h	Up to 10 days; Reported course 7–10 days.

Cat

Use / stage	Dose	Route	Schedule	Instructions
Bacterial infection	5 mg/kg	PO, IV	Every 12 h
Bacterial infection	10 mg/kg	PO	Every 24 h
Hemoplasmosis	10 mg/kg	PO	Every 24 h	Up to 7 days
Chlamydial or mycoplasmal infection	10–15 mg/kg	PO	Every 24 h
Chlamydial or mycoplasmal infection	5 mg/kg	PO	Every 12 h
Systemic bacterial infection	5–11 mg/kg	PO, IV	Every 12 h
Ehrlichiosis or anaplasmosis	5–10 mg/kg	PO	Every 12 h	Up to 21 days
Toxoplasmosis	5–10 mg/kg	PO	Every 12 h	Up to 28 days

Bird

Use / stage	Dose	Route	Schedule	Instructions
Bacterial infection	25 mg/kg	PO	Every 12 h	Up to 21 days
Drinking-water medication	Reference only	PO		400 mg doxycycline hyclate per liter as the sole drinking water source; actual intake varies, so this is not a direct mg/kg calculation.
Chlamydiosis	35 mg/kg	PO	Every 24 h	Up to 21 days; Experimentally infected cockatiels; oral suspension delivered into the crop. This study course is not interchangeable with other avian protocols.
Chlamydiosis	40–50 mg/kg	PO	Every 24 h	Cockatiels, Senegal parrots, blue-fronted and orange-winged Amazons; conventional treatment course is 45 days.
Chlamydiosis	25 mg/kg	PO	Every 24 h	African grey parrots, Goffin cockatoos, blue-and-gold and green-winged macaws; conventional treatment course is 45 days.
Injectable chlamydiosis course	Reference only	IM		75–100 mg/kg every 5–7 days for four weeks, then every five days through a 45-day course. Alternative weekly regimens use 100 mg/kg, or 75 mg/kg in macaws and lovebirds, with the specified avian injectable product. Injectable preparations are not automatically interchangeable.

Horse

Use / stage	Dose	Route	Schedule	Instructions
Bacterial infection	20 mg/kg	PO	Every 12 h	Do not use in: IV administration
Lawsonia intracellularis infection	20 mg/kg	PO	Every 24 h	Up to 21 days
Granulocytic anaplasmosis	10 mg/kg	PO	Every 12 h	Up to 14 days; Alternative to oxytetracycline; reported course 10–14 days. Do not use IV doxycycline in horses.

Chinchilla

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	2.5–5 mg/kg	PO	Every 12 h	Do not use in: Young growing animals, Pregnancy

Gerbil

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	2.5–5 mg/kg	PO	Every 12 h	Do not use in: Young growing animals, Pregnancy

Guinea Pig

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	2.5–5 mg/kg	PO	Every 12 h	Do not use in: Young growing animals, Pregnancy

Hamster

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	2.5–5 mg/kg	PO	Every 12 h	Do not use in: Young growing animals, Pregnancy

Mouse

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	2.5–5 mg/kg	PO	Every 12 h	Do not use in: Young growing animals, Pregnancy
Mycoplasmal pneumonia	Reference only	PO		Doxycycline 5 mg/kg every 12 hours with enrofloxacin 10 mg/kg every 12 hours.

Rat

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	2.5–5 mg/kg	PO	Every 12 h	Do not use in: Young growing animals, Pregnancy
Mycoplasmal pneumonia	Reference only	PO		Doxycycline 5 mg/kg every 12 hours with enrofloxacin 10 mg/kg every 12 hours.

Ratite

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	2–3.5 mg/kg	PO	Every 12 h

Reptile

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	10 mg/kg	PO	Every 24 h	Up to 45 days; Described courses range from 10–45 days; tortoise suspected mycoplasmal respiratory infection uses four weeks.

Indications

Treatment of susceptible canine ehrlichiosis, anaplasmosis, rickettsiosis and Lyme borreliosis.
Treatment of feline hemoplasmosis caused by susceptible hemotropic Mycoplasma species.
Treatment of Chlamydia felis-associated conjunctivitis and selected Mycoplasma respiratory infections in cats.
Treatment of selected susceptible bacterial respiratory or soft-tissue infections in dogs and cats, including some Bordetella infections.
Reduction of Wolbachia during treatment of canine heartworm disease as part of a complete heartworm protocol.
Treatment of selected vector-borne bacterial infections in horses, including equine granulocytic anaplasmosis.

Contraindications

Never administer IV to horses.
Do not inject IM or SC.
Avoid during pregnancy when alternatives are suitable.

Interactions

Aluminum, iron, calcium and other cations may reduce absorption.

Adverse effects

Vomiting, diarrhea and enteritis
Esophagitis and stricture after dry tablets/capsules in cats
Fatal reactions with equine IV use

Preparations

Preparation	Form	Strength	Route
Doxycycline 20 mg	Tablet	20 mg / tablet	PO
Doxycycline 50 mg	Tablet	50 mg / tablet	PO
Doxycycline 75 mg	Tablet	75 mg / tablet	PO
Doxycycline 100 mg	Tablet	100 mg / tablet	PO
Doxycycline 150 mg	Tablet	150 mg / tablet	PO
Doxycycline 50 mg capsule	Capsule	50 mg / capsule	PO
Doxycycline 100 mg capsule	Capsule	100 mg / capsule	PO
Doxycycline oral suspension 10 mg/mL	Oral Liquid	10 mg / mL	PO
Doxycycline injection 100 mg vial Doxycycline-equivalent content; reconstitute and further dilute. Never use IV in horses.	Injection	100 mg / vial	IV
Doxycycline injection 200 mg vial Reconstitute and further dilute. Never IM/SC or IV in horses.	Injection	200 mg / vial	IV

Monitoring and Administration

Always follow feline solid oral doses with water or food. Hyclate is particularly irritating if retained in the esophagus.

For IV use in suitable species, reconstitute then further dilute, commonly to 1 mg/mL, and infuse over 1–2 hours.

Monitor response and use susceptibility testing for ordinary bacterial infections; Enterobacterales and Pseudomonas are often resistant.

Aqueous compounded suspension stability is formulation dependent and can be short; a particular Ora-Plus/Ora-Sweet mixture retained potency for only 7 days. Darkening can indicate degradation.