Azithromycin Dihydrate

Macrolide antibiotics are classified by the size of the macrocyclic lactone ring of aglycone as 14-, 15- or 16-membered ring macrolides. Macrolides are characterized by similar chemical structures, mechanisms of action and resistance, but vary in the different pharmacokinetic parameters, and spectrum of activity. Azithromycin (abbrev: AZM), the first azalide macrolide, is chemically synthesized from erythromycin [E0751], with a methyl-substituted nitrogen atom incorporated into the acid-stable lactone ring, thus making the 15-membered lactone ring. AZM is marginally less active than erythromycin in vitro against Gram-positive organisms, but is more active than erythromycin and clarithromycin [C2220] against many Gram-negative pathogens including Haemophilus influenzae and Neisseria gonorrhoeae, and Mycoplasma pneumoniae. However, erythromycin-resistant organisms are also resistant to AZM. AZM is subsequently slowly released, reflecting its long terminal phase elimination half-life relative to that of erythromycin. AZM inhibits protein synthesis in susceptible organisms by binding to specific nucleotides in 23S rRNA within the 50S subunit of the bacterial ribosome.