阿奇霉素-Azithromycin
Azithromycin (Overview)
Azithromycin is a semisynthetic azalide macrolide antibiotic. Its dihydrate form is a white crystalline powder.
⸻
Storage
Commercial tablets should be stored below 30 °C.
For oral suspension preparations, store the dry product between 5–30 °C. Once reconstituted with water, multidose products may be stored at 5–30 °C for up to 10 days, after which they should be discarded. Single-dose packages should be used immediately after reconstitution.
Injectable products should be stored below 30 °C.
After reconstitution with sterile water for injection, the resulting 100 mg/mL solution remains stable for 24 hours at temperatures below 30 °C.
Azithromycin injection is compatible with many IV solutions, including 0.45% sodium chloride, normal saline, 5% dextrose, lactated Ringer’s solution, 5% dextrose with 0.3% or 0.45% sodium chloride, and 5% dextrose in lactated Ringer’s. When diluted in 250–500 mL of these solutions, it remains physically and chemically stable for 24 hours at room temperature or for 7 days when refrigerated at 5 °C.
⸻
Pharmacology / Indications / Pharmacokinetics
Like other macrolide antibiotics, azithromycin inhibits protein synthesis by penetrating susceptible bacterial cells and binding to the 50S ribosomal subunit. It is bacteriostatic in action.
It has a relatively broad antimicrobial spectrum. In vitro (without proven clinical efficacy), it is active against:
•Gram-positive bacteria such as Streptococcus pneumoniae, Staphylococcus aureus
•Gram-negative bacteria such as Haemophilus influenzae, Bordetella spp.
•Mycoplasma pneumoniae, Borrelia burgdorferi, Toxoplasma gondii, and others
Azithromycin’s broad spectrum and favorable pharmacokinetics make it useful for treating infections in various animal species. However, published veterinary data are limited. It has been shown to be ineffective against Mycoplasma pneumoniae in cats.
Pharmacokinetics:
•Dogs: Oral bioavailability ~97%. After multiple doses, tissue concentrations may not reflect plasma levels; tissue half-life can reach 90 hours. More than 50% of the administered dose is excreted unchanged in bile.
•Cats: Oral bioavailability ~58%. Tissue half-life is shorter than in dogs — 13 hours in adipose tissue and 72 hours in cardiac muscle. As in dogs, most of the drug is excreted unchanged in bile.
Compared with erythromycin, azithromycin has better absorption, longer tissue half-life, and higher concentrations in tissues and leukocytes.
⸻
Safety
Azithromycin is contraindicated in animals allergic to macrolide antibiotics and should be used with caution in animals with hepatic impairment.
At high doses, it may cause vomiting in dogs. Gastrointestinal side effects are generally milder than those of erythromycin. Other adverse effects, especially hepatic-related reactions, may occur in dogs and cats.
Local injection site reactions have been observed after IV administration.
⸻
Dosage
Dogs:
For infections caused by susceptible organisms:
•5–10 mg/kg orally once daily for 3–5 days
•5 mg/kg orally once daily for 2 days, then every 3–5 days at the same dose
•For skin infections: 5–10 mg/kg orally once daily for 5–7 days
•For animals difficult to medicate daily, a single dose every 5 days may be used after the initial 5–7 days of therapy
•For pyoderma: 10 mg/kg orally once daily for 5–10 days
•For adjunct therapy in Babesia gibsoni (Asian strain):
•Azithromycin 10 mg/kg orally once daily for 10 days
•Combined with Atovaquone 13.5 mg/kg orally three times daily, administered with fatty food, for 10 days
⸻
Source: Veterinary Drug Manual
Compiled and Published by: Mao Pipi Veterinary Care