What is the recommended dosing for azithromycin (Zithromax)?

Azithromycin Dosing Recommendations

The recommended azithromycin dosing varies by indication, with standard adult regimens including 500 mg on day 1 followed by 250 mg daily for days 2-5 for most respiratory infections, or a single 1 gram dose for certain sexually transmitted infections. 1

Adult Dosing Regimens

Respiratory and Skin Infections

• For community-acquired pneumonia (mild severity), pharyngitis/tonsillitis (second-line therapy), and uncomplicated skin/skin structure infections: 500 mg as a single dose on day 1, followed by 250 mg once daily on days 2 through 5 1
• For acute bacterial exacerbations of chronic obstructive pulmonary disease (mild to moderate): 500 mg daily for 3 days OR 500 mg on day 1, followed by 250 mg once daily on days 2 through 5 1
• For acute bacterial sinusitis: 500 mg daily for 3 days 1

Sexually Transmitted Infections

• For non-gonococcal urethritis and cervicitis: One single 1 gram dose 1, 2
• For gonococcal urethritis and cervicitis: One single 2 gram dose 1
• For chancroid (genital ulcer disease): One single 1 gram dose 1

Special Indications

• For cat scratch disease: 500 mg on day 1 followed by 250 mg for 4 additional days (for patients >45 kg) 2
• For bronchiolitis obliterans syndrome in lung transplant recipients: 250 mg per day for 5 days and then 250 mg three times per week for at least 3 months 2
• For babesiosis (in combination with atovaquone): 500-1000 mg on day 1 and 250 mg once per day thereafter orally; for immunocompromised patients, higher doses of 600-1000 mg per day may be used 2

Pediatric Dosing Regimens

Acute Otitis Media

• 30 mg/kg as a single dose, OR
• 10 mg/kg once daily for 3 days, OR
• 10 mg/kg on day 1 followed by 5 mg/kg/day on days 2 through 5 1, 2

Acute Bacterial Sinusitis

• 10 mg/kg once daily for 3 days 1

Community-Acquired Pneumonia

• 10 mg/kg on day 1 followed by 5 mg/kg on days 2 through 5 1, 2

Pharyngitis/Tonsillitis

• 12 mg/kg once daily for 5 days (for children ≥2 years) 1, 3

Pertussis Treatment and Prophylaxis

• Infants <6 months: 10 mg/kg per day for 5 days 2
• Infants and children >6 months: 10 mg/kg (maximum: 500 mg) on day 1, followed by 5 mg/kg per day (maximum: 250 mg) on days 2-5 2

Cat Scratch Disease

• Patients <45 kg: 10 mg/kg on day 1 and 5 mg/kg for 4 more days 2

Administration Considerations

• Azithromycin tablets can be taken with or without food 1
• If taken with aluminum or magnesium-containing antacids, absorption may be reduced 2
• For patients with renal impairment (GFR ≤80 mL/min), no dosage adjustment is recommended 1
• Caution should be exercised when administering to patients with severe renal impairment (GFR <10 mL/min) 1
• No dose adjustment recommendations can be made for patients with impaired hepatic function 1

Common Side Effects and Precautions

• Common side effects include abdominal discomfort/pain, diarrhea, nausea, vomiting, headache, and dizziness 2
• Monitor patients when azithromycin is used concomitantly with agents metabolized by the cytochrome P450 enzyme system 2
• Azithromycin is classified as an FDA Pregnancy Category B drug 2
• Azithromycin is preferred over erythromycin in infants <1 month due to lower risk of infantile hypertrophic pyloric stenosis 2

Clinical Pearls

• The unique pharmacokinetics of azithromycin allow for shorter treatment courses compared to other antibiotics due to high tissue concentrations and prolonged half-life 4, 5
• Single-dose regimens have the advantage of improved compliance and directly observed therapy 2, 6
• For persistent non-gonococcal urethritis after first-line doxycycline, consider azithromycin 500 mg on day 1, followed by 250 mg daily for 4 days 2
• A single 1.5 g dose of azithromycin may be an alternative to the standard 3-day regimen for atypical pneumonia in outpatients 7

Remember that appropriate dosing should be selected based on the specific indication, patient characteristics, and local resistance patterns to ensure optimal outcomes.