Azithromycin
Azithromycin is an oral and parenteral macrolide antibiotic used in adults and children for respiratory, skin and selected sexually transmitted bacterial infections. It has a long tissue half-life that supports short or single-dose courses.
- Chemical formula
- C38H72N2O12
- CAS number
- 83905-01-5
- ATC code
- J01FA10
- Molecular weight
- 748.98 g/mol
- Drug class
- Macrolide antibiotic
- Also known as
- CP-62993, Azitromicina
What is it?
Azithromycin is a 15-membered azalide derivative of erythromycin developed in the 1980s. It is supplied as oral tablets, capsules, oral suspension and parenteral solution. Azithromycin is dispensed only on prescription and is part of the World Health Organization List of Essential Medicines. Its tissue distribution and long intracellular half-life allow short oral courses (often three to five days) compared with traditional twice or thrice daily macrolides.
Mechanism of action
Azithromycin reversibly binds the 50S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis. It is generally bacteriostatic, although it can be bactericidal at high concentrations against some organisms. Its spectrum covers many Gram-positive cocci, atypical respiratory pathogens such as Mycoplasma pneumoniae, Chlamydophila pneumoniae and Legionella, and selected sexually transmitted pathogens such as Chlamydia trachomatis. Resistance via ribosomal methylation and efflux pumps is increasing in some regions.
Pharmacokinetics
Azithromycin is well absorbed orally, with bioavailability of approximately 37%. Plasma protein binding is variable (7% to 50%) and decreases with concentration. Tissue concentrations exceed plasma levels by orders of magnitude, particularly in macrophages. The terminal half-life is approximately 68 hours, supporting short courses with prolonged effective tissue exposure. Elimination is mostly biliary, with limited renal excretion. Hepatic impairment requires caution.
Indications
Azithromycin is approved in adults and children for the treatment of respiratory tract infections, otitis media, skin and soft tissue infections, and sexually transmitted infections caused by susceptible organisms, including non-gonococcal urethritis. It is also used in Mycobacterium avium complex prophylaxis and treatment in selected patients. According to clinical guidelines, choice of antibiotic should consider local resistance patterns, particularly for community-acquired respiratory infections.
Safety profile
Common adverse effects are gastrointestinal: nausea, diarrhoea and abdominal discomfort. Hepatotoxicity, hearing changes with prolonged or high-dose therapy, and QT-interval prolongation with risk of torsades de pointes have been reported, particularly in patients with electrolyte disturbances or other QT-prolonging drugs. According to the prescribing information, baseline cardiac risk and concomitant medications must be reviewed by a clinician before any prescription, especially in older adults and those with cardiovascular disease.
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Frequently asked questions
Why is azithromycin often given for only three to five days? ▾
Azithromycin has a long intracellular half-life of approximately 68 hours, with sustained tissue concentrations after the last oral dose. This allows clinical effect for several days after a short course, particularly in respiratory infections. According to the prescribing information, three or five-day regimens are common; longer or single-dose regimens are used in selected sexually transmitted infections and prophylactic indications.
Does azithromycin prolong the QT interval? ▾
Yes, in some patients. Azithromycin can prolong the QT interval and rare cases of torsades de pointes have been reported, particularly with electrolyte disturbances, bradycardia, congenital long QT syndrome or concomitant QT-prolonging medications. According to the prescribing information and regulatory communications, the prescriber should review individual cardiac risk before any prescription, particularly in older adults and patients with cardiovascular disease.
Can azithromycin be used in pregnancy? ▾
Azithromycin is generally considered acceptable during pregnancy when needed, including for selected sexually transmitted infections. Animal studies have not shown teratogenicity at therapeutic doses. According to obstetric guidelines and the prescribing information, the choice between azithromycin, amoxicillin and other antibiotics depends on the indication, gestational age and local resistance patterns. Self-medication during pregnancy should always be avoided.
Is azithromycin still effective for community-acquired pneumonia? ▾
Azithromycin remains a recognised option for atypical pathogens in community-acquired pneumonia, including Mycoplasma pneumoniae and Chlamydophila pneumoniae. However, macrolide resistance among Streptococcus pneumoniae has been rising in many regions, which is why combination therapy or alternative agents may be preferred. According to clinical guidelines, the choice depends on severity, comorbidity and local resistance patterns.
What are the main contraindications for azithromycin? ▾
Azithromycin is contraindicated in known hypersensitivity to azithromycin or any macrolide and in a history of cholestatic jaundice or hepatic dysfunction associated with prior macrolide use. Caution is required in QT-prolonging conditions or medications, severe hepatic impairment, myasthenia gravis and elderly patients. According to the prescribing information, the medical history must be reviewed by a clinician before any prescription.
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