What is the recommended dose of Keflex (cephalexin) for pediatric patients?

Pediatric Cephalexin Dosing

For most pediatric infections, cephalexin should be dosed at 25-50 mg/kg/day divided into 3-4 doses, but for methicillin-susceptible Staphylococcus aureus (MSSA) skin and soft tissue infections, use the higher range of 75-100 mg/kg/day in 3-4 divided doses to avoid underdosing. 1

Standard Dosing by Indication

Routine Infections (Streptococcal pharyngitis, uncomplicated skin infections)

• 25-50 mg/kg/day divided every 6-8 hours (QID) or every 12 hours (BID) 2, 3
• The FDA label supports both QID and BID dosing for streptococcal pharyngitis and skin infections in children over 1 year of age 3
• For streptococcal infections, continue treatment for at least 10 days 3

MSSA Skin and Soft Tissue Infections

• 75-100 mg/kg/day divided into 3-4 doses 1
• This higher dosing is critical—the Infectious Diseases Society of America specifically warns against underdosing MSSA infections with the standard 25-50 mg/kg/day range 1
• Cephalexin is the preferred oral agent for MSSA in pediatrics due to suspension availability and less frequent dosing requirements compared to dicloxacillin 2

Otitis Media

• 75-100 mg/kg/day in 4 divided doses 3
• Clinical studies demonstrate this higher dose is required for adequate middle ear penetration 3

Severe Infections

• Dosage may be doubled from the standard range 3
• If daily doses exceed 4 grams are needed, consider parenteral cephalosporins 3

Practical Dosing Examples (from FDA Label)

For 25-50 mg/kg/day regimen:

• 10 kg child: 1/2 to 1 tsp of 125 mg/5 mL QID or 1 to 2 tsp BID 3
• 20 kg child: 1 to 2 tsp of 125 mg/5 mL QID or 2 to 4 tsp BID 3
• 40 kg child: 2 to 4 tsp of 125 mg/5 mL QID or 4 to 8 tsp BID 3

Important Clinical Considerations

Dosing Frequency Options

• Four times daily (QID) remains the FDA-approved standard 3
• Three times daily (TID) at 45 mg/kg/dose (maximum 1.5 g) achieves equivalent pharmacodynamic targets with 99% cure rates in bone and joint infections 4
• Twice daily (BID) dosing can be used for streptococcal pharyngitis and uncomplicated skin infections in children over 1 year 3

Allergy Considerations

• Cephalexin is appropriate for penicillin-allergic patients except those with immediate hypersensitivity reactions 2, 1
• Cross-reactivity with penicillins is low due to cephalexin's chemical stability 5

Neonatal Dosing

• The standard pediatric doses are NOT appropriate for neonates 1
• Refer to specialized neonatal dosing guidelines for this population 1

Common Pitfalls to Avoid

Underdosing MSSA Infections

• Do not use 25-50 mg/kg/day for documented or suspected MSSA infections 1
• The 75-100 mg/kg/day range is essential for adequate tissue penetration and bacterial eradication 1

Inappropriate Use for MRSA

• Cephalexin has NO activity against methicillin-resistant Staphylococcus aureus (MRSA) 1
• If MRSA is suspected or confirmed, switch to clindamycin, trimethoprim-sulfamethoxazole, or other MRSA-active agents 2

Renal Impairment

• Reduce dosage proportionally in patients with creatinine clearance <30 mL/min 5
• 70-100% of the dose is renally excreted within 6-8 hours 5

Storage and Stability

• Reconstituted suspension must be refrigerated and discarded after 14 days 3
• Shake well before each use 3

Duration of Therapy

• Standard duration is typically 7 days for most infections 1
• Minimum 10 days for β-hemolytic streptococcal infections 3
• 7-14 days for uncomplicated cystitis 3