Zithromax, Azithromycin


  • Tablets: 250 mg, 600 mg
  • Oral Suspension: 100 mg/5mL, 200 mg/5mL
  • Powder for injection: 500 mg


Azithromycin, an azolide, is a subclass of the macrolide antibiotics. It is derived from erythromycin, but its chemical structure differs slightly by having a methyl-substituted nitrogen atom in the lactone ring. Azithromycin has the ability to block protein synthesis.

This drug is primarily bacteriostatic, but can be bactericidal depending on the concentration given. It is effective against aerobic Gram-positive microorganisms (e.g., Staphylococcus aureus, Streptococcus agalactiae, Streptococcus pneumoniae, Streptococcus pyogenes), and some Gram-negative organisms (e.g., Haemophilus spp, Moraxella catarrhalis). However, azithromycin does not appear to have any inherent direct activity against Pseudomonas aeruginosa (a Gram-negative, rod-shaped, opportunistic pathogen). Other susceptible organisms are Chlamydophila pneumoniae, Chlamydia trachomatis, and Mycoplasma.

Azithromycin is absorbed both widely and rapidly throughout the body. When distributed in the body, concentrations are found to be greater in tissue compared to that of plasma and serum levels. Although it has been shown to cross the placenta studies have not, as yet demonstrated any teratogenic effects in animals.

Due to azithromycin’s high oral bioavailability, long half-life, and ability to attain high tissue concentrations, it lends itself to a once daily dosing regimen.

The drug undergoes some hepatic (liver) metabolism with the majority of the drug being excreted in bile, and to a lesser extent in urine.


Use for infections brought about by mycobacterium, mycoplasma, chlamydia, and rickettsia.

Appears to be more effective with acute outbreaks in younger rats.

When given in older rats, for chronic respiratory infection, the addition of another suitable antibiotic
(e.g., doxycycline) may be required in combination with azithromycin.

Drug Interactions or Contraindications

  • Decreased absorption with aluminum and magnesium containing drugs.
  • Increased effect/toxicity levels when used with digoxin, and theophylline.
  • Do not give when there is impaired liver function.

Adverse Reactions

EENT: ototoxicity

GI: diarrhea, loss of appetite

GU: nephritis

Other: stroke

Dosage Recommendations

4 mg/lb to 8 mg/lb BID first 14 days then SID for additional 14 days if needed. 4
Safe for use in the pregnant Doe, and rats under 4 months. 4, 14


15 mg/kg to 30 mg/kg, PO, q24hr  34, 35, 38, 41, 43, 44.


50 mg/kg, PO, q12hr. For 14 days.  41, 42, 44..


  • Drug recommendation is to give on empty stomach (1 to 2 hours before meal or 2 hours after meals) to prevent interference with absorption of the antibiotic.
    Some drugs are known to be better absorbed without food, but unless a rat is in a hospital environment, we realize that this is impossible for the pet rat owner. It is believed to be far more important to get the medication into the rat, even if you have to mix it in a favorite food, than to worry about whether food will hinder the medications absorption rate.
  • May cause superinfections when used over long period of time.
  • Can be used simultaneously with amoxicillin or amoxicillin/clavulanate, or doxycycline.
  • *Note: some reports have indicated a limited response in older rats with more chronic or advanced problems. The drug is reported to be more effective when used in young rats.
  • Recent studies with humans, both adult and pediatric, indicate that single dose, or high dose day one with lower dose day 2 to 5 appear equally as effective in treating certain disease processes. Side effects were more commonly reported with single and short term dosing.
  • Store tablets at dry, room temperature in closed container.
  • Reconstituted oral suspension good for 10 days stored at room temperature, or as directed.

  1. Buck, M. (2005). Pediatric therapy update: azithromycin. Pediatric Pharmacotherapy: A Monthly Newsletter for Health Care Professionals from the University of Virginia Children’s Hospital, 11(4), 1-4. Retrieved December 12, 2008, from — Archived page from 2008-05-09 (via the Wayback Machine)
  2. Zithromax® (azithromycin tablets) and (azithromycin for oral suspension). (n.d.). Retrieved December 12, 2008, from


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