ZITHROMAX

Indications

• Community-acquired pneumonia
• Acute bacterial sinusitis
• Streptococcal pharyngitis
• Skin and soft tissue infections
• Chlamydia trachomatis infections
• Mycobacterium avium complex prophylaxis

Dosage

Children: Refer to the BNF for Children for specific dosing information based on the child's weight and condition.

Adults: For most infections, the usual adult dose is 500 mg on the first day, followed by 250 mg once daily for 4 days.

Mechanism of action

Azithromycin binds to the 50S subunit of the bacterial ribosome, inhibiting RNA-dependent protein synthesis. This action disrupts the translation process, preventing bacteria from synthesizing proteins necessary for their growth and replication.

Pharmacodynamics

Azithromycin exhibits bacteriostatic activity against a range of pathogens, including Streptococcus pneumoniae, Haemophilus influenzae, and Mycoplasma pneumoniae. The drug has a long half-life, allowing for once-daily dosing and shorter treatment regimens. Its tissue penetration is high, allowing effective concentrations to be achieved in the lungs and other tissues.

Pharmacokinetics

Azithromycin is well absorbed following oral administration, with a bioavailability of approximately 37%. It is extensively distributed throughout the body, with a volume of distribution of approximately 31 L/kg. The drug is primarily metabolized in the liver via the cytochrome P450 system, with a small percentage excreted unchanged in urine. The elimination half-life is around 68 hours, which supports its prolonged therapeutic effect.

Contra-indications

• Hypersensitivity to azithromycin, erythromycin, or any macrolide antibiotic
• History of cholestatic jaundice or hepatic dysfunction associated with azithromycin

Adverse effects

• Gastrointestinal disturbances (nausea, vomiting, diarrhea, abdominal pain)
• Rash
• Eosinophilia
• QT interval prolongation
• Hepatic dysfunction
• Angioedema
• Anaphylaxis

Interactions

• Caution with drugs that prolong the QT interval (e.g. antiarrhythmics, antipsychotics)
• Increased risk of warfarin toxicity due to inhibition of hepatic metabolism
• May increase plasma concentrations of certain antihistamines and statins

Precautions

• Renal impairment
• Hepatic impairment
• History of arrhythmias
• Monitor for signs of superinfection

Pregnancy

Azithromycin is classified as category B. Animal studies have not shown harm, but controlled studies in pregnant women are lacking.

Breast-feeding

Azithromycin is excreted in breast milk, but the effects on a nursing infant are not well studied. Use with caution.

Storage

Store below 30°C. Protect from light. Keep out of reach of children.

Formulations

• Oral tablets: 250 mg, 500 mg
• Oral suspension: 100 mg/5 mL, 200 mg/5 mL