Why is this medication prescribed?
Azithromycin is used to treat certain bacterial infections, such as bronchitis; pneumonia; sexually transmitted diseases (STD); and infections of the ears, lungs, sinuses, skin, throat, and reproductive organs. Azithromycin also is used to treat or prevent disseminated Mycobacterium avium complex (MAC) infection [a type of lung infection that often affects people with human immunodeficiency virus (HIV)]. Azithromycin is in a class of medications called macrolide antibiotics. It works by stopping the growth of bacteria.

Antibiotics such as azithromycin will not work for colds, flu, or other viral infections. Using antibiotics when they are not needed increases your risk of getting an infection later that resists antibiotic treatment.

Pharmacology
Mechanism of Action
Binds to 50S ribosomal subunit of susceptible microorganisms and blocks dissociation of peptidyl tRNA from ribosomes, causing RNA-dependent protein synthesis to arrest; does not affect nucleic acid synthesis

Concentrates in phagocytes and fibroblasts, as demonstrated by in vitro incubation techniques; in vivo studies suggest that concentration in phagocytes may contribute to drug distribution to inflamed tissues

Absorption
Absolute bioavailability: 38% (250-mg capsules)

Peak plasma concentration
Oral (3-day regimen): 0.44 mcg/mL (Day 1); 0.54 mcg/mL (Day 3)
Oral (5-day regimen): 0.43 mcg/mL (Day 1); 0.24 mcg/mL (Day 5)
IV: 1.14 mcg/mL (healthy volunteers); 3.63 mcg/mL (hospitalized patients)
AUC
Oral (3-day regimen): 17.4 mcg⋅hr/mL
Oral (5-day regimen): 154.9 mcg⋅hr/mL
IV: 8.03 mcg⋅hr/mL (healthy volunteers); 9.6 mcg⋅hr/mL (hospitalized patients)
Effects of food
Oral suspension: When administered with food, peak plasma concentration increased by 56% and AUC unchanged
Tablets: No effect
Distribution
Protein bound: 51% (0.02 mcg/mL); 7% (2 mcg/mL)

Elimination
Clearance: 630 mL/min (single 500-mg oral and IV dose)

Half-life
Oral (3-day regimen): 71.8 hr
Oral (5-day regimen): 68.9 hr
Excretion
IV, 1st dose: 11%
IV, 5th dose: 14%
Oral: 6% (unchanged)
Biliary excretion is a major route of elimination for unchanged drug, following oral administration