What is the recommended dose of azithromycin (Zithromax) for various infections?

Azithromycin Dosing Recommendations

For adults with community-acquired pneumonia, the standard regimen is 500 mg on day 1, followed by 250 mg once daily on days 2-5, while for sexually transmitted infections a single 1-2 gram dose is appropriate, and pediatric dosing is weight-based at 10 mg/kg (max 500 mg) on day 1, then 5 mg/kg (max 250 mg) daily for days 2-5. 1

Adult Dosing by Indication

Respiratory Tract Infections

• Community-acquired pneumonia (mild severity): 500 mg as a single dose on day 1, followed by 250 mg once daily on days 2-5 (total 5-day course) 1, 2
• Alternative 3-day regimen: 500 mg once daily for 3 consecutive days 1, 2
• Acute bacterial exacerbations of COPD: Either 500 mg daily for 3 days OR the standard 5-day regimen (500 mg day 1, then 250 mg daily days 2-5) 1
• Acute bacterial sinusitis: 500 mg once daily for 3 days 1
• Pharyngitis/tonsillitis (second-line therapy): 500 mg day 1, then 250 mg daily days 2-5 1

Sexually Transmitted Infections

• Non-gonococcal urethritis and cervicitis: Single 1 gram dose 1
• Genital ulcer disease (chancroid): Single 1 gram dose 1
• Gonococcal urethritis and cervicitis: Single 2 gram dose 1

Skin and Soft Tissue Infections

• Uncomplicated skin/skin structure infections: 500 mg day 1, then 250 mg daily days 2-5 1, 3
• Alternative studied regimen: 500 mg once daily for 3 days 3

Hospitalized Patients

• Intravenous azithromycin for admitted patients: 500 mg daily for 2-5 days, followed by oral therapy at 500 mg daily for a total of 7-10 days 2
• This IV regimen has demonstrated efficacy even in patients with pneumococcal bacteremia 2

Pediatric Dosing (Age ≥6 months)

Standard 5-Day Regimen

• Community-acquired pneumonia and acute otitis media: 10 mg/kg (maximum 500 mg) as a single dose on day 1, followed by 5 mg/kg (maximum 250 mg) once daily on days 2-5 1, 4
• This regimen is recommended by both the American Academy of Pediatrics and the Infectious Diseases Society of America 4

Alternative 3-Day Regimen

• Acute otitis media and acute bacterial sinusitis: 10 mg/kg once daily for 3 consecutive days 1

Single-Dose Regimen

• Acute otitis media only: 30 mg/kg as a single dose (maximum 1,200 mg) 1
• If vomiting occurs within 30 minutes, re-dosing at the same total dose has been studied, though safety data are limited 1

Pharyngitis/Tonsillitis (Age ≥2 years)

• Higher dose required: 12 mg/kg once daily for 5 days 1, 5
• This higher dose is necessary because standard dosing resulted in more recurrences compared to penicillin 5

Pertussis Treatment and Prophylaxis

• Infants <6 months: 10 mg/kg once daily for 5 days 4
• Children ≥6 months: 10 mg/kg (max 500 mg) day 1, then 5 mg/kg (max 250 mg) daily days 2-5 4
• Azithromycin is preferred over erythromycin in young infants due to better safety profile 4

Intravenous Pediatric Dosing

• IV azithromycin: 10 mg/kg once daily (maximum 500 mg per dose) on days 1-2, then transition to oral therapy when clinically feasible 4
• Prolonged IV therapy beyond 2 days should be avoided when oral therapy is tolerated 4

Weight-Based Dosing Table (for 5-day regimen)

• 5 kg (11 lbs): 2.5 mL day 1, then 1.25 mL days 2-5 (using 100 mg/5 mL suspension) 1
• 10 kg (22 lbs): 5 mL day 1, then 2.5 mL days 2-5 1
• 20 kg (44 lbs): 5 mL day 1, then 2.5 mL days 2-5 (using 200 mg/5 mL suspension) 1
• 30 kg (66 lbs): 7.5 mL day 1, then 3.75 mL days 2-5 1
• 40 kg (88 lbs): 10 mL day 1, then 5 mL days 2-5 1
• ≥50 kg (≥110 lbs): 12.5 mL day 1, then 6.25 mL days 2-5 1

Special Populations

Renal Impairment

• GFR 10-80 mL/min: No dosage adjustment required 1
• GFR <10 mL/min: Exercise caution as AUC increases by 35%; however, no specific dose adjustment is established 1

Hepatic Impairment

• Pharmacokinetics have not been established in hepatic impairment 1
• No dose adjustment recommendations can be made 1

Age and Gender

• No dosage adjustment required based on age or gender alone 1

Administration Considerations

Food Effects

• Adults and children: Azithromycin tablets and oral suspension can be taken with or without food 1
• However, coadministration with a large meal may reduce absorption by up to 50% 6

Drug Interactions

• Avoid concurrent administration with aluminum- or magnesium-containing antacids as they reduce absorption 4, 1
• If antacids are necessary, separate administration times 4
• Monitor when used with drugs metabolized by cytochrome P450 enzyme system 4
• Monitor for QT interval prolongation when combined with other QT-prolonging medications 4

Clinical Pearls and Common Pitfalls

Atypical Pathogens

• Azithromycin provides excellent coverage for atypical respiratory pathogens including Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella species 2, 5
• For severe community-acquired pneumonia, azithromycin should be combined with a beta-lactam active against drug-resistant Streptococcus pneumoniae 2

Tolerance Profile

• Gastrointestinal adverse effects (nausea, diarrhea, abdominal pain) are the most common but generally mild to moderate 4, 5
• Azithromycin has better gastrointestinal tolerance than erythromycin 4, 5, 6

Resistance Considerations

• Azithromycin is active against erythromycin- and penicillin-susceptible S. pneumoniae and methicillin-susceptible S. aureus 5
• In areas with high rates of resistant S. pneumoniae, consider alternative agents or combination therapy 2

Infantile Hypertrophic Pyloric Stenosis (IHPS)

• In infants under 1 month, azithromycin has not been associated with IHPS, though monitoring is recommended 4
• The benefits of treating severe pertussis outweigh potential risks in this age group 4

Pregnancy Classification

• FDA Pregnancy Category B 4