Azithromycin, Azithromycin extended release, Zithromax, Zmax

  • Azithromycin is a macrolide antibiotic used to treat a wide range of clinical conditions, including bacterial conjunctivitis, upper respiratory tract bacterial infections, some patients with bacterial community-acquired pneumonia (CAP), disseminated Mycobacterium avium complex (MAC), pertussis, Chlamydia, gonococcal STDs, and cat scratch disease.
  • Mechanism of resistance: Methylation of ribosomal target and activation of efflux pump.
  • Various pharmaceutical preparations:
    • Oral tabs: 250 mg, 500 mg, 600 mg
    • Oral single-dose suspension: 1 gm
    • Oral extended release (ER) suspension: 2 gm
    • Pediatric immediate-release suspension: 100 mg/5 mL and 200 mg/5 mL
    • Ophthalmic solution, 1%
    • Powder for reconstitution and IV use, 500 mg vials
  • Evaluate risk of prolongation of QTc before prescribing; details under adverse effects
Bacterial conjunctivitis Azithromycin ophthalmic solution 1 drop bid x 2 days,
then 1 drop once daily x 5 days
Respiratory tract, skin, skin structure
(mild/moderate infection)
500 mg po day 1,
then 250 mg once daily, days 2-5
Community-acquired pneumonia (CAP) 500 mg IV once daily
(often combined with beta-lactam)
Chancroid 1 gm po single dose
C. trachomatis 1 gm po single dose
N. gonorrhoeae 2 gm po single dose
HIV+ with disseminated MAC 600 mg po daily + Ethambutol
MAC prophylaxis in AIDS patients: 1200 mg po once weekly

  • Age > 28 days
Oral Dose 5-12 mg/kg/day (once daily)
IV Dose 10 mg/kg/day (once daily)

  • None
  • None

  • Treatment stopped due to adverse effects (1%), rash (rare), neutropenia (rare), thrombocytopenia (rare), nausea/vomiting (3%), diarrhea (5%), increased LFTs (rare), increased BUN/Creatinine (rare).
  • Variety of other laboratory abnormalities (e.g., lymphopenia, eosinophilia, electrolytes and liver function abnormalities), which may or may not be drug related, have been reported at a frequency of 1% or less.
  • Transient reversible hearing loss from Azithromycin (J Otolaryngol 36:257, 2007).
  • QTc interval prolongation: Any of the macrolides (Azithromycin, Clarithromycin, and Erythromycin) have the potential of increasing the QTc interval and predispose to ventricular tachycardia.
    • QTc prolongation may be congenital or acquired (NEJM 358:169, 2008). Variable prevalence of mutations associated with long QT: 11% in Denmark vs. 20% in New Zealand or Minnesota (J Cardiovasc Electrophysiol 23:1092, 2012).
    • In retrospective controlled study from Tennessee, 5 days of Azithromycin increased the risk of cardiovascular death (hazard ratio 2.88, p 0.001); compared to Amoxicillin, estimated 47 additional cardiovascular deaths per 1 million courses of therapy (NEJM 366:1881, 2012). Subsequent larger study in generally younger population from Denmark showed CV mortality in Azithromycin recipients was only 15.4/million courses vs. 85.2/million courses in the Tennessee study (NEJM 368:1704, 2013; NEJM 368:1665, 2013).

    • Risk of ventricular arrhythmia and/or cardiac death studied in 2 million Taiwanese outpatients treated within 7 days with amox/clav, oral FQ, or oral macrolide (Azithromycin/Clarithromycin). Although the number of events was low, compared to Amoxicillin-Clavulanate, the highest propensity score adjusted odds ratios were 2.74 for Moxifloxacin, and 3.4 for Azithromycin (Clin Infect Dis 60: 566, 2015).
    • Hence, Azithromycin may increase risk of CV death in patients with congenital or acquired cardiovascular disease risk factors. Caution indicated in patients with history of unexplained syncope, family history of unexplained sudden cardiac death, known electrolyte abnormalities, or the need for concomitant administration of other drugs known to potentially prolong the QTc.

    • Full listing of  drugs with the potential to prolong the QTc available at or
    • Prolonged QTc defined as > 470 ms for men; > 480 ms for women, and > 500 ms for either men or women.
    • Review with balance of benefits vs risk see Am J Med 128: 1362.e1, 2015

Agent is a first line therapy: reliably active in vitro, clinically effective, guideline recommended, recommended as a first-line agent or acceptable alternative agent in the Sanford Guide

Active + ( 17 )

Agent is a potential alternative agent (active in vitro, possesses class activity comparable to known effective agents or a therapeutically interchangeable agents and hence likely to be clinically effective, but second line due to overly broad spectrum, toxicity, limited clinical experience, or paucity of direct evidence of effectiveness)

note: Mycoplasma species are generally susceptible to azithromycin and other macrolides. The exception is Mycoplasma hominis which is resistant to macrolides.

Class Azalide
PK/PD Index 24-hr AUC/MIC
Tabs (250, 500, 600 mg)
Susp (1 gm single dose)
Peds susp (100 mg/5 ml, 
200 mg/5 ml)
Adult ER susp (2 gm) Injection
Usual Adult Dose Varies 2 gm po x1 500 mg IV q24h
Food Effect1 Take with or without food Take without food Not applicable
Absorption2 (%)
37 Approx 30 Not applicable
Peak Serum Level3
0.4 (500 mg po SD) 0.8 (2 gm po SD) 3.6 (500 mg IV SD)
Protein Binding
7-51 7-51 7-51
Average Serum
Half-life4 (hr)
68 59 68
Biliary Penetration5 (%) High High High
Penetration6 (%)
No data No data No data
Therapeutic Levels in CSF7 No data No data No data
Volume of Distribution8
31.1 L/kg 31.1 L/kg 33.3 L/kg
4.3 (500 mg po x1) 20 (2 gm po x1) 9.6 (AUC0-24,
CYP450, Transporter
Substrate of: PGP
Inhibits: PGP (weak)
Tmax (hr)10 2.5 5.0 No data
  • Notes:
    • 1 Adult preparations unless otherwise noted.
    • 2 Absorption under optimal conditions.
    • 3 Total drug; adjust for protein binding to determine free drug concentration.
      • SD = after single dose
      • SS = steady state after multiple doses
    • 4 Assumes CrCl > 80 mL/min
    • 5 Peak concentration in bile/peak concentration in serum x 100
    • 6 CSF levels with inflammation
    • 7 Judgment based on drug dose & organism susceptibility. CSF concentration ideally ≥10x above MIC.
    • 8 Volume of Distribution (Vd):
      • V/F = Vd/oral bioavailability
      • Vss = Vd at steady state
      • Vss/F = Vd at steady state/oral bioavailability
    • 9 Area under the plasma concentration versus time curve
    • 10 Time from administration to maximum plasma concentration

Azithromycin (A) Agent B Effect  
  Cyclosporine ↑ serum levels of B with toxicity +
  Digoxin, digitoxin ↑ serum levels of B (10% of cases) +
  Pimozide ↑ Q-T interval ++
  • +, ++ indicates relative importance.

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