What is the appropriate antibiotic dosage for a 9-year-old boy weighing 55kg with suspected streptococcal pharyngitis?

Antibiotic Dosage for Streptococcal Pharyngitis in a 9-Year-Old Boy Weighing 55kg

For a 9-year-old boy weighing 55kg with suspected streptococcal pharyngitis, the recommended first-line treatment is amoxicillin at a dose of 50 mg/kg once daily (maximum 1000 mg) for 10 days.

Diagnostic Approach

Before prescribing antibiotics, confirm the diagnosis using:

1. Clinical assessment with Centor Criteria:

   • Tonsillar exudates
   • Tender anterior cervical lymph nodes
   • Lack of cough
   • Fever

2. Rapid antigen detection test (RADT) and/or throat culture for patients with 3-4 Centor criteria 1

First-Line Treatment Options

Amoxicillin (Preferred)

• Dosage: 50 mg/kg once daily (maximum 1000 mg)
• Since the patient weighs 55kg, the daily dose would be 1000 mg (capped at maximum)
• Duration: 10 days
• Advantages: Once-daily dosing improves compliance compared to multiple daily doses 1

Penicillin V (Alternative first-line)

• Dosage: 500 mg twice daily or 250 mg three times daily
• Duration: 10 days 2, 1

Alternative Options for Penicillin-Allergic Patients

For Non-Anaphylactic Penicillin Allergy:

• Cephalexin: 20 mg/kg twice daily (maximum 500 mg per dose) for 10 days 2
• Cefadroxil: 30 mg/kg once daily (maximum 1 g) for 10 days 2

For Immediate-Type Hypersensitivity:

• Clindamycin: 7 mg/kg three times daily (maximum 300 mg per dose) for 10 days 2
• Azithromycin: 12 mg/kg once daily (maximum 500 mg) for 5 days 2, 3
  • For this 55kg patient, the dose would be 12 mg/kg = 660 mg, capped at 500 mg daily
• Clarithromycin: 7.5 mg/kg twice daily (maximum 250 mg per dose) for 10 days 2

Important Considerations

1. Complete the full course: It's crucial to complete the full 10-day course (except for azithromycin which is 5 days) to prevent acute rheumatic fever and ensure complete eradication of Group A Streptococcus 1

2. Resistance concerns: Be aware that macrolides (azithromycin, clarithromycin) may have resistance rates of 20-25% in some regions 2, 4

3. Symptomatic treatment: In addition to antibiotics, recommend:

   • NSAIDs or acetaminophen for pain and fever
   • Warm salt water gargles
   • Throat lozenges 1

4. Follow-up: If symptoms worsen after 72 hours of treatment or persist for 5 days after starting antibiotics, reevaluation is necessary 4

Caution

For this 9-year-old weighing 55kg (which is above the typical weight for this age), use the maximum pediatric dose rather than calculating based on exact weight, as this would exceed recommended maximums. The 1000 mg daily maximum for amoxicillin is appropriate in this case 1.