DogSource: Sykes 2003
5–10 mg/kg · once daily · 3–5 days
Antibiotic Therapy
Azithromycin
Macrolide (azalide) · bacteriostatic, protein-synthesis inhibitor (50S ribosome)
Species: Dogs & Cats9 dose protocols6 dosage forms
This page is a calculation and educational reference for veterinarians and veterinary students. It does not replace examination, culture and susceptibility testing, clinical judgment, or the attending veterinarian's final decision.
Drug overview
Macrolide (azalide) · bacteriostatic, protein-synthesis inhibitor (50S ribosome)
Brand names: Zithromax®
General dose: 5–10 mg/kg PO · once dailySource: Plumb's (general)
Spectrum of activity
A macrolide (azalide), bacteriostatic, with very high tissue penetration and a long half-life; its strength is intracellular/atypical and respiratory bacteria — Chlamydia, Mycoplasma, Bordetella, Haemophilus — as well as Campylobacter, Helicobacter, streptococci and susceptible staph. It also covers spirochetes (Borrelia) and the intracellular Rhodococcus and Mycobacterium avium complex. But it is not reliable against Enterobacteriaceae (E. coli), Pseudomonas, enterococci and anaerobes. ⚠️ It is ineffective against Mycoplasma haemofelis (feline hemotropic mycoplasma).
Veterinary uses and doses
General (susceptible) infection
CatSource: Sykes 2003
Cat: 5–10 mg/kg · once daily · 3–5 days
Skin (pyoderma / dermatology)
DogSource: Merchant 2000
Dermatology: 5–10 mg/kg · once daily · 3–5 days
DogSource: Ramadinha 2002
Pyoderma: 10 mg/kg · once daily · 5–10 days
CatSource: Merchant 2000
Cat (dermatology): 7–15 mg/kg · every 12 h · 5–7 days
Upper respiratory infection (URI)
CatSource: Scherk 2006
Cat: 5–10 mg/kg daily × 5 days, then every 72 h (long-term)
Clinical note: For feline chlamydial infection (Chlamydia felis), doxycycline (10 mg/kg daily, about 4 weeks) is first-line; azithromycin is reported to be less effective at clearing Chlamydia and is more of an alternative.
Babesiosis (B. gibsoni)
DogSource: Birkenheuer 2004
10 mg/kg · once daily · 10 days
Combination therapy: with atovaquone 13.3 mg/kg every 8 h with a fatty meal; both drugs for 10 days
Pulse (extended-interval) dosing
DogSource: Aucoin 2002
5 mg/kg · days 1 and 2 daily, then one dose every 3–5 days (5 doses total)
CatSource: Aucoin 2002
Cat: 5 mg/kg · days 1 and 2 daily, then one dose every 3–5 days (5 doses total)
Dosage forms
- Suspension 200 mg/5 mL
- Suspension 100 mg/5 mL
- Capsule 250 mg
- Capsule 500 mg
- Tablet 250 mg
- Tablet 500 mg
Safety and clinical notes
- Use with caution in hepatic impairment (metabolism and excretion are mainly hepatic-biliary).
- The most common adverse effects are GI (vomiting, especially with high doses, and diarrhea); but less than with erythromycin.
- Absorption is reduced by magnesium- or aluminium-containing antacids; separate by about 2 hours.
- It may raise cyclosporine and digoxin levels; use with caution alongside them.
- Do not refrigerate the oral suspension, shake well before each use, and give preferably on an empty stomach; discard the reconstituted suspension after 14 days.
- It has a very long tissue half-life; this is what makes once-daily and pulse (extended-interval) regimens possible.
- ⚠️ It is ineffective against Mycoplasma haemofelis (feline hemotropic mycoplasma); use doxycycline for that.
Cited sources
- Plumb's (general)
- Sykes 2003
- Merchant 2000
- Ramadinha 2002
- Scherk 2006
- Birkenheuer 2004
- Aucoin 2002
Calculate a weight-based dose
Drug-data last updated: