Azithromycin exerts its antibacterial effect by inhibiting bacterial protein synthesis. According to the Lippincott Textbook of Pharmacology, azithromycin binds to the 50S ribosomal subunit of susceptible bacteria, leading to:

• Inhibition of translocation during protein synthesis.
• Prevention of the addition of new amino acids to the growing peptide chain.
• Bacteriostatic effect (inhibition of bacterial growth) at low concentrations and bactericidal effect (killing of bacteria) at higher concentrations.

The Lange Basic & Clinical Pharmacology further explains that azithromycin has a unique pharmacokinetic profile, allowing it to achieve high concentrations in tissues and cells, which enhances its effectiveness against intracellular pathogens such as Chlamydia and Legionella.

Azithromycin is indicated for the treatment of a wide range of bacterial infections, including:

1. Respiratory Tract Infections:
   • Community-acquired pneumonia.
   • Acute bacterial sinusitis.
   • Acute exacerbations of chronic obstructive pulmonary disease (COPD).
   • Pharyngitis and tonsillitis (as an alternative to penicillin).
2. Skin and Soft Tissue Infections: Such as cellulitis and impetigo.
3. Sexually Transmitted Infections (STIs):
   • Chlamydia trachomatis infections.
   • Non-gonococcal urethritis and cervicitis.
4. Mycobacterial Infections: As part of combination therapy for Mycobacterium avium complex (MAC) in HIV patients.
5. Traveler's Diarrhea: Caused by susceptible enteric pathogens.
6. Otitis Media: In pediatric patients.

The British National Formulary (BNF) emphasizes that azithromycin should only be used for infections caused by susceptible organisms and is ineffective against viral infections.

The dosage of azithromycin varies depending on the type and severity of the infection, the patient's age, and renal function. The following are general guidelines:

Oral Administration

• Community-Acquired Pneumonia: 500 mg once daily for 3 days or a single 2 g dose.
• Acute Bacterial Sinusitis: 500 mg once daily for 3 days.
• Skin and Soft Tissue Infections: 500 mg on day 1, followed by 250 mg once daily on days 2-5.
• Chlamydia Infections: A single 1 g dose.
• Mycobacterium avium Complex (MAC) Prophylaxis: 1.2 g once weekly.

Intravenous Administration

• Severe Infections: 500 mg once daily for at least 2 days, followed by oral therapy to complete the course.

Pediatric Dosage

• Otitis Media: 10 mg/kg once daily for 3 days or a single 30 mg/kg dose.
• Pharyngitis/Tonsillitis: 12 mg/kg once daily for 5 days.

Renal Impairment

• No dose adjustment is required for mild to moderate renal impairment. Use with caution in severe renal impairment.

Azithromycin is generally well-tolerated, but it may cause side effects. Common side effects, as listed in the Lippincott Textbook of Pharmacology, include:

• Gastrointestinal Issues: Nausea, vomiting, diarrhea, and abdominal pain.
• Headache: Mild to moderate.
• Skin Reactions: Rash or itching.

Less common but serious side effects may include:

• Hepatotoxicity: Liver dysfunction, indicated by jaundice or elevated liver enzymes.
• QT Prolongation: Leading to an increased risk of arrhythmias.
• Allergic Reactions: Such as angioedema or anaphylaxis.
• Clostridioides difficile-Associated Diarrhea (CDAD): Due to disruption of normal gut flora.

Patients experiencing severe side effects should seek medical attention immediately.

Before starting azithromycin, certain precautions should be taken:

1. Allergy to Macrolides: Azithromycin is contraindicated in patients with a history of hypersensitivity to macrolide antibiotics.
2. Liver Disease: Use with caution in patients with hepatic impairment, as azithromycin is metabolized in the liver.
3. QT Prolongation: Avoid in patients with a history of arrhythmias or those taking other QT-prolonging drugs.
4. Myasthenia Gravis: Azithromycin may exacerbate muscle weakness in patients with myasthenia gravis.
5. Pregnancy and Breastfeeding: Azithromycin is generally considered safe during pregnancy and breastfeeding, but should only be used if clearly needed and under medical supervision.
6. Pediatric Use: Safe for use in children, but dosing should be based on body weight.

Azithromycin may interact with other medications, potentially altering their effects or increasing the risk of side effects. Key interactions highlighted in the BNF and Lange Basic & Clinical Pharmacology include:

• Antacids: May reduce the absorption of azithromycin. Administer azithromycin 1 hour before or 2 hours after antacids.
• Warfarin: Azithromycin may enhance the anticoagulant effect of warfarin, increasing the risk of bleeding.
• QT-Prolonging Drugs: Such as amiodarone, fluoroquinolones, or antipsychotics, which may increase the risk of arrhythmias.
• Cyclosporine: Azithromycin may increase cyclosporine levels, increasing the risk of toxicity.
• Digoxin: Azithromycin may increase digoxin levels, increasing the risk of toxicity.

Always inform your healthcare provider about all medications, supplements, and herbal products you are taking before starting azithromycin.

Azithromycin is the active ingredient in the brand-name medication Zithromax. In pharmacies, it may also be available under various generic names, including:

• Azithromycin Dihydrate
• Azithromycin Monohydrate
• Azithromycin Tablets/Suspension