Cephalexin Dosing for Wound Infection in Hemodialysis Patients
For a patient on hemodialysis with a wound infection, administer oral cephalexin 250–500 mg immediately after each dialysis session (three times weekly), rather than using daily dosing.
Dosing Algorithm
Standard Hemodialysis Regimen
- Give cephalexin 250–500 mg orally after each dialysis session (typically Monday, Wednesday, Friday schedule) 1
- Administer immediately after dialysis completion to prevent premature drug removal during the next session 1
- Do not reduce the individual dose size; instead, extend the dosing interval to three times weekly 2
Rationale for Post-Dialysis Timing
- Hemodialysis removes approximately 58% of cephalexin from serum over a 6-hour session 3
- Post-dialysis administration ensures adequate therapeutic levels throughout the interdialytic period 1
- Cephalexin achieves peak serum concentrations within 1 hour in most patients, though delayed absorption (6–12 hours) occurs in some dialysis patients 3
Pharmacokinetic Considerations
Drug Clearance in Dialysis
- In anephric patients, cephalexin demonstrates prolonged serum half-life with high, sustained concentrations after single doses 3
- Patients with creatinine clearance <30 mL/min require proportional dose reduction based on residual renal function 4
- However, for hemodialysis patients, maintain full individual doses (250–500 mg) while extending the interval to three times weekly 2, 1
Urinary Concentrations
- Even with impaired renal function, cephalexin achieves urinary concentrations of 500–1000 mcg/mL following 250–500 mg oral doses 4
- These concentrations far exceed the minimum inhibitory concentration for common wound pathogens including Staphylococcus aureus, Streptococcus pyogenes, and E. coli 4
Alternative Considerations
When IV Therapy Is Required
- For serious wound infections requiring intravenous therapy, cefazolin 20 mg/kg IV after each dialysis session is preferred over oral cephalexin 5
- Cefazolin demonstrates superior pharmacokinetics in dialysis patients with validated dosing schedules 5
Comparative Efficacy
- For wound infections in dialysis patients, β-lactams like cephalexin are appropriate first-line agents when the pathogen is susceptible 2
- Unlike UTIs where cephalexin is considered alternative therapy, wound infections caused by gram-positive organisms respond well to cephalosporin therapy 2
Critical Pitfalls to Avoid
Common Dosing Errors
- Never use daily dosing (e.g., 500 mg four times daily) in hemodialysis patients, as this leads to dangerous drug accumulation 2, 4
- Avoid reducing individual dose size to 125 mg or lower, as this produces subtherapeutic peak concentrations and treatment failure 2
- Do not administer before dialysis, as the drug will be removed before achieving therapeutic effect 1
Safety Monitoring
- Therapeutic drug monitoring of serum cephalexin concentrations is recommended to verify adequate exposure while avoiding accumulation 2
- Monitor for hypersensitivity reactions, though cephalexin has a low incidence of allergy due to its chemical stability 4
Agents to Avoid
- Aminoglycosides (gentamicin, tobramycin) should not be used as first-line therapy for wound infections in dialysis patients due to substantial risk of irreversible ototoxicity 2
- While aminoglycosides are dosed at 1 mg/kg after each dialysis session for catheter-related infections, they carry a 4% nephrotoxicity rate with 25% irreversibility 5, 1
Duration of Therapy
- For uncomplicated wound infections, treat for 7–14 days (approximately 7–14 doses over 2.3–4.7 weeks on a thrice-weekly schedule)
- Adjust duration based on clinical response, wound healing, and absence of systemic signs of infection