A macrolide antibiotic.

It inhibits bacterial growth, probably by blocking dissociation of peptidyl tRNA from ribosomes, causing RNA-dependent protein synthesis to arrest.

While plasma concentrations are very low, tissue concentrations are much higher, making this agent valuable in the treatment of infections caused by intracellular organisms.

Has a long tissue half-life.

An azalide, a subclass of macrolide antibiotics.

Derived from erythromycin.

It has a similar antimicrobial spectrum as erythromycin, but is more effective against certain Gram-negative bacteria, in particular, Haemophilus influenzae.

Azithromycin is used to treat bacterial infections causing middle ear infections, streptococcal throat infections, sinusitis, nonstreptococcal bacterial pharyngitis, traveler’s diarrhea, respiratory tract infections such as pneumonia, cellulitis, babesiosis, Bartonella infection, chancroid cholera, donovanosis, leptospirosis, Lyme disease, malaria, Mycobacterium avium complex disease, Neisseria meningitis, pelvic inflammatory disease, pertussis, scrub typhus, toxoplasmosis, and salmonellosis.

It is used to prevent bacterial endocarditis.

Useful in dental infections.

Has been used primarily to prevent bacterial infections in infants and in those with immune deficiencies.

Effective against certain sexually transmitted infections, such as nongonococcal urethritis, chlamydia, and cervicitis.

Resistance has been described to this and other macrolide antibiotics.

Infants who received azithromycin in the early days of life are at an increased risk for developing infantile hypertrophic pyloric stenosis (IHPS).

In a retrospective analysis, among 163 infants given azithromycin in the first 14 days of life, about 2% developed IHPS (Eberly M et al).

The link was strongest if exposure to the antibiotic occurred in the first 2 weeks of life.

Side effects are gastrointestinal and include diarrhea, nausea, abdominal pain, and vomiting, with fewer than 1% of patients stop taking the drug due to side effects.

Pseudomembranous colitis can occur during and up to several weeks after use.

May interfere with the effectiveness of birth control agents.

Interferes with bacterial protein synthesis by binding to the 50S subunit of the bacterial ribosome, and inhibiting translation of DNA.

Existing QT prolongation, bradycardia, and low blood levels of magnesium or potassium are risk factors associated with exacerbation of QT prolongation and lead to torsades de pointes, a potentially lethal form of arrhythmia.

Chlamydia pneumoniae, Chlamydia trachomatis,, Escherichia coli, Haemophilus influenzae, Moraxella catarrhalis, Neisseria gonorrhoeae are generally susceptible.

Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pyogenes are resistant to azithromycin.

Acid-stable, and it is readily absorbed, but its absorption is greater on an empty stomach.

Has a high concentration in phagocytes, which allows active transport to the site of infection.

During active phagocytosis the concentration of azithromycin in the tissues can be over 50 times higher than in plasma.

Prolonged half-life allows single daily dose to maintain bacteriostatic levels in the infected tissue for several days.

There is a warning against long-term use of azithromycin to prevent bronchiolitis obliterans syndrome in patients with blood or lymph node cancers who have received donor stem cell transplants.

This use of azithromycin can lead to increased risk of cancer relapse and death in this population.

Patients with blood or lymph node cancers are at an increased risk of bronchiolitis obliterans syndrome after donor stem cell transplant; although azithromycin is not approved for prevention of this condition, the antibiotic is sometimes prescribed for that purpose.

Following a single 500 mg dose, the half-life of azithromycin is 11–14 hours, and a longer half-life of 68 hours is achieved when multiple doses are used.

Biliary excretion mostly unchanged, is a major route of elimination.

Approximately 6% of the drug appears as unchanged in urine. . Trade name, Zithromax.

Available as, a 1% ophthalmic formulation of azithromycin, for the treatment of eye infections.

Most commonly administered in tablet or oral suspension.

Available for intravenous injection.

Tablets come in doses of 250 mg and 500 mg.

Oral suspension comes in strengths of 100 mg/5 ml and 200 mg/5 ml.

The 250-mg tablets are often dispensed in packages of six and commonly referred to as a “Z-Pak”.

A double dose of medication is administered on the first day of treatment and subsequent treatment for four or five additional days.

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