What is the appropriate cephalexin dose for a child weighing 27 kg with normal renal function?

Cephalexin Dosing for a 27 kg Child

For a child weighing 27 kg with normal renal function, administer cephalexin 675 mg (approximately 13.5 mL of 250 mg/5 mL suspension) every 8 hours, or alternatively 337.5 mg (approximately 6.75 mL) every 6 hours, depending on infection severity.

Standard Dosing Framework

The FDA-approved pediatric dosing range for cephalexin is 25–50 mg/kg/day divided into doses, with the specific regimen determined by infection type and severity 1.

Mild to Moderate Infections (Standard Dose)

• 25–50 mg/kg/day is appropriate for most common infections including uncomplicated skin infections, pharyngitis, and urinary tract infections 1.
• For a 27 kg child, this translates to:
  • 675–1,350 mg total daily dose
  • Divided every 12 hours: 337.5–675 mg per dose (approximately 6.75–13.5 mL of 250 mg/5 mL suspension twice daily) 1
  • Divided every 6 hours: 168.75–337.5 mg per dose (approximately 3.4–6.75 mL four times daily) 1

Severe Infections or Otitis Media (High Dose)

• 75–100 mg/kg/day in 4 divided doses is required for otitis media and severe infections 1.
• For a 27 kg child with otitis media:
  • 2,025–2,700 mg total daily dose
  • Divided every 6 hours: 506.25–675 mg per dose (approximately 10–13.5 mL of 250 mg/5 mL suspension four times daily) 1

Infection-Specific Recommendations

Methicillin-Susceptible Staphylococcus aureus (MSSA) Infections

• The Infectious Diseases Society of America recommends 75–100 mg/kg/day divided into 3 or 4 doses for MSSA infections 2.
• For a 27 kg child: 2,025–2,700 mg/day, which equals 506.25–675 mg every 6 hours or 675–900 mg every 8 hours 2.

Streptococcal Pharyngitis

• For Group A streptococcal pharyngitis, the total daily dose may be divided and administered every 12 hours 1.
• A dose of 337.5–675 mg twice daily (approximately 6.75–13.5 mL of 250 mg/5 mL suspension) is appropriate 1.
• Continue treatment for at least 10 days for β-hemolytic streptococcal infections 1.

Urinary Tract Infections

• For uncomplicated cystitis in patients over 15 years, 500 mg every 12 hours is standard; however, for younger children, use 50–100 mg/kg/day divided into 4 doses 2, 1.
• For a 27 kg child: 337.5–675 mg every 6 hours 1.

Practical Dosing Algorithm

Step 1: Identify infection severity and type

• Mild/moderate (pharyngitis, uncomplicated skin infection, UTI) → 25–50 mg/kg/day
• Severe or otitis media → 75–100 mg/kg/day

Step 2: Calculate total daily dose for 27 kg child

• Mild/moderate: 675–1,350 mg/day
• Severe/otitis media: 2,025–2,700 mg/day

Step 3: Select dosing frequency

• Every 12 hours (twice daily) for pharyngitis and skin infections 1
• Every 6–8 hours (3–4 times daily) for severe infections, MSSA, or otitis media 2, 1

Step 4: Convert to suspension volume (using 250 mg/5 mL)

• Mild infection, twice daily: 6.75–13.5 mL per dose
• Severe infection, four times daily: 10–13.5 mL per dose

Important Clinical Considerations

Maximum Dosing Limits

• If daily doses greater than 4 g are required, parenteral cephalosporins should be considered instead 1.
• For a 27 kg child, even the highest recommended dose (100 mg/kg/day = 2,700 mg/day) remains well below this threshold 1.

Duration of Therapy

• β-hemolytic streptococcal infections require at least 10 days of treatment to prevent rheumatic fever 1.
• Cystitis should be treated for 7–14 days 1.
• For MSSA infections, duration depends on infection site and severity, typically 7–14 days for uncomplicated cases 2.

Renal Impairment

• Cephalexin is 70–100% renally excreted within 6–8 hours 3.
• Patients with creatinine clearance <30 mL/min require dose reduction proportional to reduced renal function 3.
• The question specifies normal renal function, so no adjustment is needed 3.

Storage and Preparation

• After reconstitution, store suspension in refrigerator 1.
• Suspension may be kept for 14 days without significant loss of potency 1.

Common Pitfalls to Avoid

• Underdosing otitis media: Many clinicians use standard 25–50 mg/kg/day dosing, but otitis media specifically requires 75–100 mg/kg/day for adequate middle ear penetration 1.
• Inadequate treatment duration for streptococcal infections: Stopping antibiotics when symptoms resolve (typically 3–4 days) rather than completing the full 10-day course risks rheumatic fever 1.
• Using cephalexin for inappropriate pathogens: Cephalexin is not appropriate for pneumococcal pneumonia (use amoxicillin 90 mg/kg/day instead), β-lactamase-producing organisms, or MRSA 2.
• Forgetting to adjust for severe infections: The standard 25–50 mg/kg/day dose is insufficient for severe infections; double the dose to 75–100 mg/kg/day 1.