Azithromycin: veterinary dose and monograph

At a glance

Drug class

Antibiotic

Also known as

Zithromax, Azee, Azithral

Species with doses

Dogs, Cats, Horses, Birds, Rabbits and Guinea pigs

General dose range

5–10 mg/kg PO q24h then q48–72h — check the species tables for the indication

Routes

PO

Last reviewed

1 October 2026

Indications

• Respiratory infections (Bordetella, atypical pneumonia)
• Feline bartonellosis and Chlamydophila
• Foal Rhodococcus equi pneumonia (with rifampin)
• Avian chlamydiosis

Azithromycin dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Respiratory / soft-tissue infection: Plumb’s p.138: 5–10 mg/kg PO once daily for 3–5 days (Trepanier; Sykes); pyoderma 10 mg/kg once daily for 5–10 days; Babesia gibsoni 10 mg/kg once daily with atovaquone 13.3 mg/kg q8h for 10 days. Papich 5e: 10 mg/kg once daily for 5–7 days, then every other day; or 5 mg/kg/day.

Cats

• Bartonella / Chlamydophila / URI: Plumb’s p.138: 5–10 mg/kg PO once daily for 3–5 days; URI 5–10 mg/kg once daily for 5 days then every 3rd day for 6–8 weeks (Scherk 2006); Bartonella 10 mg/kg once daily for 21 days. Papich 5e: 5–10 mg/kg once daily for 7 days then q48h; URI 15 mg/kg daily for 3 days then q72h.

Horses

• Foal R. equi pneumonia: Papich 5e and Plumb’s p.138 (Jacks 2001): 10 mg/kg PO once daily for 5 days, then every other day once responding. Usually combined with rifampin. Adult horses (Papich): 10 mg/kg PO q48h — watch for colitis in adults.

Birds

• Chlamydiosis: Plumb’s p.138 (Guzman 2010): experimentally infected cockatiels — 40 mg/kg PO every other day for 21 days, as effective as 21 or 45 days of doxycycline; dosed by crop tube with the human oral suspension.

Rabbits

• Jaw abscess / osteomyelitis: Plumb’s p.138: jaw abscesses 15–30 mg/kg PO once daily for 2–4 weeks after surgery (Johnson 2006); Staphylococcus osteomyelitis 50 mg/kg PO once daily with rifampin 40 mg/kg q12h (Ivey & Morrisey 2000). Stop if anorexia or diarrhoea develops.

Guinea pigs

• Pneumonia: Plumb’s p.138 (Johnson 2006): guinea pigs 15–30 mg/kg PO once daily. Stop if soft stools develop.

Contraindications

Macrolide hypersensitivity. Hepatic impairment (hepatic metabolism). Caution with QT-prolonging drugs. Adult horses — risk of severe diarrhoea (reserve for foals).

Species-specific warnings

Horses: Use only in foals — adult horses develop life-threatening colitis. Hyperthermia / anhidrosis is reported in treated foals during hot weather.

Adverse effects

• GI upset — vomiting, diarrhoea
• Hepatic enzyme elevation
• Foal hyperthermia / diarrhoea

Drug interactions

• Oral antacids (magnesium- and aluminium-containing): reduce the RATE of azithromycin absorption — separate doses by 2 hours
• Cisapride: no azithromycin-specific data, but other macrolides are contraindicated with cisapride — use with caution
• Cyclosporine: azithromycin may raise cyclosporine blood levels — monitor closely
• Digoxin: no azithromycin-specific data, but other macrolides raise digoxin levels — monitor
• Pimozide: CONTRAINDICATED — acute deaths have occurred (human drug, unlikely in veterinary practice)

Toxicity and overdose

Plumb's: acute oral overdose is unlikely to cause significant morbidity beyond vomiting, diarrhoea and GI cramping. As with all macrolides, the serious species risk is not overdose but the class effect — macrolides can precipitate fatal enterocolitis/enterotoxaemia in rabbits and other hindgut fermenters, and are contraindicated by the oral route in adult horses (Clostridium difficile colitis).

Clinical pearls

• Long tissue half-life means short courses with extended intervals — improves compliance
• For foal R. equi, combine with rifampin and watch the mare for antibiotic-associated colitis from coprophagia
• Keep dairy / food-animal use off-label and avoid — prolonged residues

Mechanism of action

Azithromycin is an azalide (macrolide subclass). Plumb's: penetrates the cell wall and binds the 50S ribosomal subunit, inhibiting bacterial protein synthesis — bacteriostatic. Relatively broad in vitro spectrum (which does not by itself prove clinical efficacy): gram-positives such as Streptococcus pneumoniae and Staph. aureus; gram-negatives such as Haemophilus influenzae; plus Bartonella spp., Bordetella spp., Mycoplasma pneumoniae, Borrelia burgdorferi and Toxoplasma spp. Its defining property is extensive tissue sequestration — tissue concentrations greatly exceed serum, giving a long tissue half-life that supports short courses and extended dosing intervals.

Formulations and products

• Azithromycin 250 mg tablet
• Azithromycin oral suspension 40 mg/mL (200 mg/5 mL after reconstitution — Plumb’s p.139)
• Azithromycin 500 mg powder vial reconstituted to 100 mg/mL (sterile water) — dilute further before IV infusion (Plumb’s p.138–139)

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other antibiotics

• Amoxicillin
• Amoxicillin / Clavulanic Acid
• Ampicillin
• Apramycin
• Cefadroxil
• Cefazolin
• Cefixime
• Cefoperazone

Frequently asked questions