What is the recommended dosage of Keflex (Cephalexin) for a 9-year-old female?

Keflex (Cephalexin) Dosing for a Nine-Year-Old Female

The recommended dosage of Keflex (cephalexin) for a 9-year-old female is 25-50 mg/kg/day divided into 2-4 doses, with a typical regimen being 250 mg four times daily or 500 mg twice daily for most infections. 1

Dosing Considerations Based on Weight and Indication

Standard Dosing

• For a 9-year-old female (assuming average weight of approximately 30 kg):
  • 25-50 mg/kg/day = 750-1500 mg total daily dose
  • Divided into 4 doses: 187.5-375 mg every 6 hours
  • Divided into 2 doses: 375-750 mg every 12 hours

Dosing by Specific Conditions

1. Streptococcal pharyngitis:

   • 25-50 mg/kg/day divided twice daily for 10 days 2
   • For a 30 kg child: 375-750 mg twice daily

2. Skin and skin structure infections:

   • 25-50 mg/kg/day divided twice daily 2
   • For a 30 kg child: 375-750 mg twice daily

3. Otitis media:

   • Higher dosage of 75-100 mg/kg/day in 4 divided doses 1
   • For a 30 kg child: 562.5-750 mg four times daily

4. Urinary tract infections:

   • 25-50 mg/kg/day divided into 3-4 doses 3
   • Duration typically 7-14 days for cystitis 1

Administration Guidelines

Formulation Options

• Oral suspension: Available as 125 mg/5 mL or 250 mg/5 mL
• Capsules: Available in 250 mg and 500 mg strengths

Practical Dosing for a 9-Year-Old (approximately 30 kg)

Using the FDA-approved dosing table 1:

• For a 30 kg child using 250 mg/5 mL suspension:
  • Four times daily dosing: 1-2 teaspoons (5-10 mL) four times daily
  • Twice daily dosing: 2-4 teaspoons (10-20 mL) twice daily

Important Clinical Considerations

Duration of Therapy

• For streptococcal pharyngitis: Complete full 10-day course to prevent rheumatic fever 2
• For skin infections: Duration depends on severity and clinical response
• For urinary tract infections: 7-14 days 1

Monitoring and Safety

• Cephalexin is generally well-tolerated in pediatric patients 4
• Monitor for gastrointestinal symptoms (most common side effect)
• Rare cases of neutropenia may occur with high-dose therapy 5

Common Pitfalls to Avoid

1. Underdosing: Insufficient dosing may lead to treatment failure
2. Inadequate duration: Particularly important for streptococcal infections
3. Not adjusting for renal impairment: Dose reduction needed if creatinine clearance <30 mL/min 4
4. Inappropriate use in penicillin-allergic patients: Avoid in patients with immediate hypersensitivity reactions to penicillin 2

Alternative Dosing Regimens

Recent research suggests that less frequent dosing may be effective:

• Twice-daily dosing: 22-45 mg/kg for susceptible S. aureus infections 6
• Three-times-daily dosing: 15-25 mg/kg for susceptible S. aureus infections 6
• Higher doses (45 mg/kg three times daily) have been shown effective and well-tolerated for bone and joint infections 5

Remember that the FDA-approved dosing remains 25-50 mg/kg/day divided into 2-4 doses, with specific adjustments based on the type and severity of infection 1.