Azithromycin
Azithromycin is a long-persisting macrolide-related antibiotic with high intracellular accumulation. It is also a partner drug in selected protozoal treatment regimens.
Group
Azalide antibacterial
Mechanism of Action
Binding to the bacterial 50S ribosomal subunit inhibits protein synthesis. Immunomodulatory effects may influence respiratory responses but do not imply susceptibility of resistant bacteria.
Dose Rates
Dog
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Susceptible bacterial infection | 10 mg/kg | PO | Every 24 h | Up to 7 days; A common initial course is five to seven days; continuation or interval extension depends on the infection. |
| Babesia gibsoni infection | 10 mg/kg | PO | Every 24 h | Up to 10 days; Combine with atovaquone 13–15 mg/kg every eight hours for ten days. |
| Susceptible bacterial infection | 5–10 mg/kg | PO | Every 24 h | Up to 5 days; Alternative initial course of three to five days. |
| Susceptible bacterial infection — intermittent course — Initial | 5 mg/kg | PO | Every 24 h | Up to 2 days; Initial two daily doses before the separate intermittent continuation. |
| Susceptible bacterial infection — intermittent course — Maintenance | 5 mg/kg | PO | Every 72–120 h | After two initial daily doses; five doses total across the course. |
| Dermatologic infection | 5–10 mg/kg | PO | Every 24 h | Up to 7 days; Initial course five to seven days; prolonged treatment may use a five-day interval in selected responsive cases. |
| Dermatologic infection — Maintenance | 5–10 mg/kg | PO | Every 120 h | Only after an initial five-to-seven-day daily course and documented response. |
| Pyoderma | 10 mg/kg | PO | Every 24 h | Up to 10 days; Described course five to ten days; culture-directed selection is important. |
| Chronic lymphoplasmacytic rhinitis | 5 mg/kg | PO | Every 24 h | Historical immunomodulatory combination with an anti-inflammatory drug; investigate the primary cause and assess benefit before prolonged treatment. |
Cat
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Susceptible bacterial infection — Initial | 5–10 mg/kg | PO | Every 24 h | Up to 7 days; For selected susceptible infections; does not reliably eradicate feline Chlamydia or Mycoplasma haemofelis. |
| Susceptible bacterial infection — Maintenance | 5–10 mg/kg | PO | Every 48 h | Continuation after the initial daily course when clinically indicated. |
| Cytauxzoonosis | 10 mg/kg | PO | Every 24 h | Up to 10 days; Combine with atovaquone 15 mg/kg every eight hours for ten days and supportive care. |
| Susceptible bacterial infection | 5–10 mg/kg | PO | Every 24 h | Up to 5 days; Alternative initial course of three to five days. |
| Susceptible bacterial infection — intermittent course — Initial | 5 mg/kg | PO | Every 24 h | Up to 2 days; Initial two daily doses before the separate intermittent continuation. |
| Susceptible bacterial infection — intermittent course — Maintenance | 5 mg/kg | PO | Every 72–120 h | After two initial daily doses; five doses total across the course. |
| Dermatologic infection | 7–15 mg/kg | PO | Every 12 h | Up to 7 days; Older alternative five-to-seven-day regimen; monitor tolerability. |
| Dermatologic infection — Maintenance | 7–15 mg/kg | PO | Every 120 h | Only after the initial five-to-seven-day course and a positive response. |
| Upper respiratory infection — Initial | 5–10 mg/kg | PO | Every 24 h | Up to 5 days |
| Upper respiratory infection — Maintenance | 5–10 mg/kg | PO | Every 72 h | Up to 56 days; After the initial five daily doses; older prolonged regimen of six to eight weeks only where a sustained response supports continuing. |
| Bartonellosis | 10 mg/kg | PO | Every 24 h | Up to 21 days; Institute flea control; reassess other causes when response is absent. |
Horse
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Rhodococcus equi infection — Initial | 10 mg/kg | PO | Every 24 h | Up to 5 days; Foals; use as part of an appropriate combination regimen, commonly with rifampin. |
| Rhodococcus equi infection — Maintenance | 10 mg/kg | PO | Every 48 h | Foals; step down after an initial response and continue the planned combination regimen. |
Rabbit
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Staphylococcal osteomyelitis | 50 mg/kg | PO | Every 24 h | Combination regimen with rifampin; monitor appetite and fecal output. Companion rifampin regimen is 40 mg/kg orally every twelve hours. |
| Jaw abscess | 15–30 mg/kg | PO | Every 24 h | Up to 28 days; Continue two to four weeks after surgery; stop and reassess with anorexia or diarrhea. |
Guinea pig
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Pneumonia | 15–30 mg/kg | PO | Every 24 h | Discontinue and reassess if soft stools or other GI intolerance develops. |
Cockatiel
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Chlamydiosis | 40 mg/kg | PO | Every 48 h | Up to 21 days; Regimen studied in experimentally infected cockatiels; oral suspension delivered into the crop. Do not extrapolate to all bird species. |
Indications
- Selected susceptible respiratory, soft-tissue and intracellular bacterial infections.
- Rhodococcus equi infection in foals in combination regimens.
- Combination treatment of canine Babesia gibsoni infection or feline cytauxzoonosis.
- Selected feline Bartonella-associated disease, rabbit jaw abscess or osteomyelitis, guinea-pig pneumonia and experimentally studied cockatiel chlamydiosis.
Contraindications
- Macrolide hypersensitivity.
- Adult horses are at risk of antimicrobial-associated diarrhea or enterocolitis.
- Not a dependable treatment for serious infections caused by resistant enteric gram-negative bacteria.
- Do not give IV concentrate as a bolus or by IM injection.
- Hepatic impairment warrants additional caution.
- Pregnancy safety is not fully established.
Interactions
- Rifampin is used in selected foal regimens but can alter drug exposure.
- Use cautiously with other QT-prolonging drugs.
- Aluminum- or magnesium-containing antacids can alter oral exposure.
- Cyclosporine and digoxin concentrations may increase; monitor when combined. Pimozide and cisapride pose additional arrhythmia concerns. Separate aluminum/magnesium antacids by about two hours.
Adverse effects
- Vomiting, diarrhea and reduced appetite.
- Diarrhea or enterocolitis in horses.
- Potential cardiac repolarization effects in susceptible patients.
Toxicity
Monitor GI tolerance, clinical response and hepatic indices when indicated. High doses increase vomiting; inappropriate macrolide exposure in adult horses can cause severe intestinal disease. Reassess antimicrobial selection if clinical response is inadequate; long tissue persistence does not compensate for organism resistance.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Zithromax 250 mg Azithromycin activity supplied as dihydrate. | Tablet | 250 mg / tablet | PO |
| Zithromax 500 mg Azithromycin activity supplied as dihydrate. | Tablet | 500 mg / tablet | PO |
| Zithromax 100 mg/5 mL oral suspension Strength after reconstitution, expressed as azithromycin activity. | Oral Liquid | 100 mg / 5 mL | PO |
| Zithromax 200 mg/5 mL oral suspension Strength after reconstitution, expressed as azithromycin activity. | Oral Liquid | 200 mg / 5 mL | PO |
| Azimax 200 DT Dispersible tablet containing azithromycin as dihydrate. | Tablet | 200 mg / tablet | PO |
