Cephalexin Dosing for Scalp Laceration in 17.4 kg Child
For a 17.4 kg child with a full-thickness scalp laceration, administer oral cephalexin 25-50 mg/kg/day divided into 3-4 doses (approximately 435-870 mg/day total, or 110-220 mg per dose if given four times daily). This targets methicillin-susceptible Staphylococcus aureus (MSSA) and Streptococcus species that commonly contaminate traumatic skin wounds 1, 2, 3.
Specific Dosing Calculation
For this 17.4 kg patient:
- Standard dosing: 25-50 mg/kg/day = 435-870 mg/day total
- Four times daily (QID): 110-220 mg per dose every 6 hours
- Three times daily (TID): 145-290 mg per dose every 8 hours
The FDA-approved dosing for skin and soft tissue infections in children is 25-50 mg/kg/day divided into 3-4 doses 3. The IDSA guidelines specifically recommend cephalexin at 25-50 mg/kg/day in 3-4 divided doses for non-purulent skin and soft tissue infections in children 1, 2.
Practical Dosing Recommendations
For optimal adherence and efficacy, consider:
- TID dosing at 30-40 mg/kg/day (approximately 175-230 mg per dose for this child) is well-supported by recent pharmacokinetic data showing adequate target attainment for MSSA with MICs ≤2 mg/L 4, 5
- QID dosing remains the FDA standard but compliance is challenging in outpatient settings 3
Recent pediatric PK/PD studies demonstrate that TID dosing at 45 mg/kg/dose (maximum 1.5 g) achieves the same pharmacodynamic targets as traditional QID dosing, with 99% cure rates in bone and joint infections 5. For this 17.4 kg child, that would be approximately 780 mg per dose TID, though this exceeds typical dosing for simple lacerations.
Duration and Clinical Context
Treat for 5-7 days depending on clinical response 1, 3. For traumatic lacerations:
- Ensure proper wound irrigation and closure
- Cephalexin covers both MSSA and streptococci, the primary pathogens in traumatic skin wounds
- If signs of systemic infection develop (fever, spreading erythema, lymphangitis), reassess for need to escalate therapy
Important Caveats
- This dosing assumes normal renal function - adjust if creatinine clearance is impaired 3
- Cephalexin is INACTIVE against MRSA - if there's concern for MRSA (prior colonization, injection drug use in household, treatment failure), switch to clindamycin or TMP-SMX 1, 2
- Prepare suspension properly: Use 125 mg/5 mL or 250 mg/5 mL suspension, refrigerate after mixing, discard after 14 days 3
- For a 17.4 kg child using 250 mg/5 mL suspension at approximately 200 mg per dose QID: give approximately 4 mL (slightly less than 1 teaspoon) four times daily
The weight-based dosing table from the FDA label suggests for a ~20 kg child: 1-2 teaspoons of 125 mg/5 mL QID or 0.5-1 teaspoon of 250 mg/5 mL QID 3, which aligns with the calculated 25-50 mg/kg/day range.