Azithromycin Capsule 250 mg Mechanism of Action

Pharmacologic category: Macrolide Antibiotic.
Pharmacology: Pharmacodynamics: Azithromycin usually is bacteriostatic, although the drug may be bactericidal in high concentrations against selected organisms. Bactericidal activity has been observed in vitro against Streptococcus pyogenes, S. pneumoniae, and Haemophilus influenzae.
Azithromycin inhibits protein synthesis in susceptible organisms by penetrating the cell wall and binding to 50S ribosomal subunits, thereby inhibiting translocation of aminoacyl transfer-RNA and inhibiting polypeptide synthesis. The site of action of azithromycin appears to be the same as that of the macrolides, clindamycin, lincomycin, and chloramphenicol. The antimicrobial activity of azithromycin is reduced at low pH. Azithromycin concentrates in phagocytes, including polymorphonuclear leukocytes, monocytes, macrophages, and fibroblasts. Penetration of the drug into phagocytic cells is necessary for activity against intracellular pathogens (e.g. Staphylococcus aureus, Legionella pneumophilia, Chlamydia trachomatis, Salmonella typhi).
Pharmacokinetics: Absorption: Azithromycin is rapidly absorbed from GI tract after oral administration. The absolute oral bioavailability of azithromycin is reported to be approximately 34-52% with single doses of 500 mg to 1.2 g administered as various conventional dosage form. Peak plasma azithromycin concentrations averaged 0.5 mcg/mL at about 2 hours. Food increased peak plasma concentration by 23%, but no effect on AUC.
Distribution: Azithromycin appears to be distributed into most body tissues and fluids after oral administration. Volume of distribution is 31.1-33.3 L/kg. Azithromycin is 51% bound to plasma proteins at drug concentrations of 0.02 mcg/mL and 7% bound at drug concentrations of 2 mcg/mL. Azithromycin crosses the placenta and is distributed into cord blood and amniotic fluid. Azithromycin is distributed into milk.
Metabolism: Azithromycin is metabolized by hepatic.
Elimination: The elimination half-life is 68 hours. The average tissue half-life is estimated to be 1-4 days. The half-life in peripheral leukocytes ranges from 34-57 hours. Azithromycin is excreted in feces principally as unchanged drug. Biliary excretion of azithromycin, predominantly as unchanged drug, is a major route of elimination following oral administration. Only a small portion of each azithromycin dose is excreted in urine (approximately 6%).