What is the recommended dosage of Keflex (Cephalexin) for pediatric patients with bacterial infections?

Keflex (Cephalexin) Dosing for Pediatric Bacterial Infections

For pediatric patients with bacterial infections, cephalexin should be dosed at 25-50 mg/kg/day divided into 3-4 doses (or every 6-12 hours depending on infection severity), with higher doses of 75-100 mg/kg/day reserved for severe infections like otitis media. 1

Standard Dosing Regimens

General Pediatric Dosing

• The FDA-approved dosage is 25-50 mg/kg/day divided into doses given every 6-12 hours 1
• For most common infections (skin/soft tissue, pharyngitis), the total daily dose can be split and given every 12 hours (twice daily) 1
• For more severe infections or less susceptible organisms, dosing should be every 6 hours (four times daily) 1

Infection-Specific Dosing

Skin and Soft Tissue Infections (MSSA):

• 25-50 mg/kg/day divided into 4 doses for methicillin-susceptible Staphylococcus aureus infections 2
• The IDSA guidelines specifically recommend this regimen for impetigo and other uncomplicated skin infections 2
• Can be given every 12 hours for streptococcal pharyngitis and uncomplicated skin infections 1

Otitis Media:

• 75-100 mg/kg/day divided into 4 doses - this higher dose is specifically required based on clinical studies 1
• This represents a critical dosing distinction; standard doses are insufficient for middle ear infections 1

Streptococcal Pharyngitis:

• 25-50 mg/kg/day, can be divided and given every 12 hours 1
• Treatment must continue for at least 10 days for β-hemolytic streptococcal infections to prevent rheumatic fever 1

Practical Dosing by Weight

The FDA label provides specific volume-based dosing for oral suspension 1:

For 125 mg/5 mL suspension (given 4 times daily):

• 10 kg child: 2.5-5 mL (½-1 teaspoon)
• 20 kg child: 5-10 mL (1-2 teaspoons)
• 40 kg child: 10-20 mL (2-4 teaspoons)

For twice-daily dosing (strep throat, uncomplicated skin infections):

• Double the individual dose volumes but give only twice daily 1

Alternative Dosing Frequencies

Recent pharmacokinetic data suggests less frequent dosing may be acceptable for certain MSSA infections:

• For MSSA osteoarticular infections: Both three times daily (TID) and four times daily (QID) dosing achieved similar clinical cure rates in retrospective data 3
• Pharmacokinetic modeling suggests: 22-45 mg/kg twice daily may achieve adequate drug levels for MSSA with MIC ≤2 mg/L, though 80 mg/kg twice daily is needed for MIC of 4 mg/L 4
• For TID dosing: 15-25 mg/kg three times daily for MSSA with MIC ≤2 mg/L 4

However, these alternative regimens have not been prospectively validated and should not replace FDA-approved dosing for most infections 4, 3

Critical Considerations and Pitfalls

Maximum Doses

• If daily doses exceeding 4 grams are required, parenteral cephalosporins should be considered instead 1
• Individual doses in older/larger children should not exceed adult dosing (typically 500 mg per dose for routine infections) 1

Duration of Therapy

• Minimum 10 days for β-hemolytic streptococcal infections (pharyngitis) to prevent complications 1
• 7-14 days for uncomplicated cystitis 1
• Longer courses for bone/joint infections after initial parenteral therapy 3

Common Prescribing Errors to Avoid

• Underdosing otitis media: Using 25-50 mg/kg/day instead of the required 75-100 mg/kg/day leads to treatment failure 1
• Inadequate duration for strep throat: Stopping before 10 days risks rheumatic fever 1
• Using cephalexin for MRSA: Cephalexin has NO activity against methicillin-resistant Staphylococcus aureus; clindamycin (30-40 mg/kg/day) should be used instead 2, 5

Formulation and Storage

• Oral suspension must be refrigerated after mixing 1
• Suspension remains stable for only 14 days after reconstitution 1
• Available as 125 mg/5 mL or 250 mg/5 mL suspensions 1

Renal Impairment

• Cephalexin is renally cleared; dose reduction is required when creatinine clearance falls below 30 mL/min 6
• Children may require higher per-kilogram doses than adults due to greater body water turnover 6

When Cephalexin is NOT Appropriate

• MRSA infections: Use clindamycin, vancomycin, or linezolid instead 2, 5
• Atypical pneumonia: Use azithromycin or doxycycline (if >8 years old) 7
• Severe infections requiring hospitalization: Consider parenteral cephalosporins (cefazolin 50 mg/kg/day IV divided every 8 hours) 2
• Penicillin allergy with immediate hypersensitivity: Cephalexin is contraindicated 2