What is the recommended dosage of cefalexin (cephalexin) for a 15kg pediatric patient?

Cephalexin Dosing for a 15kg Pediatric Patient

For a 15kg child, administer cephalexin 187.5 mg (3.75 mL of the 250mg/5mL suspension) every 6 hours for standard infections, or 281-375 mg (5.6-7.5 mL) every 6 hours for more severe infections such as MSSA skin and soft tissue infections or bone and joint infections. 1, 2

Standard Dosing Framework

The FDA-approved pediatric dosing for cephalexin is 25-50 mg/kg/day divided into doses 1. For your 15kg patient:

• Standard infections: 25 mg/kg/day = 375 mg/day divided every 6 hours = 93.75 mg per dose (approximately 2 mL of 250mg/5mL suspension)
• Moderate infections: 37.5 mg/kg/day = 562.5 mg/day divided every 6 hours = 140.6 mg per dose (approximately 2.8 mL)
• Severe infections: 50 mg/kg/day = 750 mg/day divided every 6 hours = 187.5 mg per dose (3.75 mL) 1

Higher Dosing for MSSA Infections

For methicillin-susceptible Staphylococcus aureus (MSSA) skin and soft tissue infections or bone and joint infections, use 75-100 mg/kg/day in 3-4 divided doses 2, 3. This translates to:

• 75 mg/kg/day: 1,125 mg/day = 281 mg every 6 hours (5.6 mL) or 375 mg every 8 hours (7.5 mL)
• 100 mg/kg/day: 1,500 mg/day = 375 mg every 6 hours (7.5 mL) or 500 mg every 8 hours (10 mL) 2

The Infectious Diseases Society of America specifically warns against underdosing MSSA infections and recommends using the higher 75-100 mg/kg/day range rather than the standard 25-50 mg/kg/day 2.

Alternative Dosing Frequencies

Twice-Daily Dosing

For improved adherence, 22-45 mg/kg per dose twice daily can be used for MSSA with MIC ≤2 mg/L 4. For your 15kg patient, this equals 330-675 mg twice daily (6.6-13.5 mL twice daily).

Three-Times-Daily Dosing

Recent evidence supports 45 mg/kg per dose (maximum 1.5g) three times daily for bone and joint infections 5, 6. For your 15kg patient, this equals 675 mg three times daily (13.5 mL three times daily). This regimen showed 99% cure rates in a retrospective audit of 149 children with bone and joint infections 5.

Practical Dosing Recommendations by Indication

For Streptococcal Pharyngitis or Uncomplicated Skin Infections:

• 187.5 mg (3.75 mL) every 12 hours 1
• Can use the twice-daily dosing schedule per FDA labeling for these specific indications 1

For Otitis Media:

• 281-375 mg (5.6-7.5 mL) every 6 hours (75-100 mg/kg/day in 4 divided doses) 1

For MSSA Infections:

• 375 mg (7.5 mL) every 8 hours OR 281 mg (5.6 mL) every 6 hours 2, 5

Important Clinical Considerations

Duration of therapy: Typically 7 days for most infections, with at least 10 days required for β-hemolytic streptococcal infections 2, 1.

Penicillin allergy: Cephalexin is appropriate for penicillin-allergic patients except those with immediate hypersensitivity reactions 2, 3.

Storage: After reconstitution, refrigerate and discard after 14 days 1.

Common Pitfalls to Avoid

• Do not underdose MSSA infections: Use 75-100 mg/kg/day, not the standard 25-50 mg/kg/day range 2
• Do not use for MRSA: Cephalexin is only effective against methicillin-susceptible organisms 2
• Monitor for neutropenia with high-dose regimens: While generally well-tolerated, 13 of 149 children (8.7%) developed mild neutropenia on high-dose three-times-daily regimens, though without clinical complications 5
• Gastrointestinal tolerance: High doses (45 mg/kg three times daily) caused GI symptoms in only 4 of 149 children (2.7%) 5