Azithromycin Dosing for Strep Throat
For strep throat (Group A Streptococcal pharyngitis), azithromycin should be dosed at 12 mg/kg once daily (maximum 500 mg) for 5 days. 1
Critical Dosing Information
- The 12 mg/kg dose for 5 days is specifically recommended for pharyngitis/tonsillitis, not the lower 10 mg/kg dose used for other infections 1
- Maximum daily dose is 500 mg regardless of weight 1, 2
- This higher dose was established after studies showed the 10 mg/kg dose for 3 days resulted in inferior bacteriologic eradication (only 65% vs. 82% with penicillin) 3
Weight-Based Dosing Table
Using the 200 mg/5 mL suspension for a 5-day course 2:
- 8 kg (18 lbs): 2.5 mL (½ tsp) daily = 12.5 mL total (500 mg total) 2
- 17 kg (37 lbs): 5 mL (1 tsp) daily = 25 mL total (1000 mg total) 2
- 25 kg (55 lbs): 7.5 mL (1½ tsp) daily = 37.5 mL total (1500 mg total) 2
- 33 kg (73 lbs): 10 mL (2 tsp) daily = 50 mL total (2000 mg total) 2
- ≥40 kg (88 lbs): 12.5 mL (2½ tsp) daily = 62.5 mL total (2500 mg total) 2
Important Clinical Context
Azithromycin is NOT first-line therapy for strep throat. It should only be used in patients with penicillin allergy, as it carries a "strong, moderate" recommendation compared to penicillin's "strong, high" recommendation 1
Key Limitations to Discuss with Patients:
- Macrolide resistance among Group A Streptococcus is approximately 5-8% in the United States and varies geographically 4
- Azithromycin is the only antibiotic that requires only 5 days of treatment due to its prolonged tissue half-life, while all other alternatives require 10 days 4
- Clinical success rates are comparable to penicillin (98% vs. 84%), but bacteriologic eradication at 30 days is lower (77% vs. 63%) 2
Common Pitfalls to Avoid
- Do not use the 10 mg/kg dose - this was studied and found inferior for pharyngitis 3
- Do not use the 3-day regimen - only the 5-day course at 12 mg/kg is appropriate for strep throat 1, 2
- Do not use azithromycin as first-line when penicillin or amoxicillin can be used - reserve it for true penicillin allergy 4
- Gastrointestinal side effects are more common with azithromycin (16.6%) than penicillin (1.7%), though generally mild 5
When to Consider Alternatives
If the patient has both penicillin allergy AND a history of clarithromycin allergy, azithromycin remains appropriate as these are different macrolides with distinct structures 4. However, if local macrolide resistance is high (>10%), consider clindamycin 7 mg/kg three times daily for 10 days instead 1, 4