Keflex Dosing in Hemodialysis Patients
Administer Keflex 250-500 mg after each hemodialysis session (typically 3 times per week), with the dose given immediately post-dialysis to prevent premature drug removal and ensure adequate therapeutic levels between sessions.
Dosing Principles for Hemodialysis
Cephalexin requires significant dose adjustment in end-stage renal disease (ESRD) because it is primarily eliminated by the kidneys, and hemodialysis removes approximately 58% of the drug during a 6-hour session 1.
The serum half-life of cephalexin is dramatically prolonged in anephric patients, reaching approximately 8.47 hours compared to 1.03 hours in patients with normal renal function 2.
Post-dialysis administration is critical to avoid wasting the dose through premature removal during dialysis and to facilitate directly observed therapy 1, 2.
Specific Dosing Recommendations
Standard dose: 250-500 mg administered immediately after each hemodialysis session (3 times weekly for patients on thrice-weekly dialysis schedules) 1, 2.
The 250 mg dose is appropriate for mild to moderate infections, while 500 mg may be used for more severe infections, as both doses achieve adequate serum and urinary concentrations in hemodialysis patients 1, 2.
Peak serum levels occur within 1 hour in most patients, though delayed absorption up to 6-12 hours can occur in some anephric patients, requiring clinical monitoring 1.
Clinical Monitoring Considerations
Careful clinical observation is essential as the FDA label specifically warns that cephalexin should be administered with caution in markedly impaired renal function, and safe dosage may be lower than usually recommended 3.
Monitor for drug accumulation between dialysis sessions, as the interdialytic half-life is significantly prolonged in ESRD patients 1, 2.
Watch for signs of superinfection or allergic reactions, as prolonged drug exposure increases these risks 3.
Important Caveats
Do not use standard dosing regimens (500 mg every 6-8 hours) designed for patients with normal renal function, as this will lead to dangerous drug accumulation 2.
Avoid administering cephalexin before dialysis sessions, as this results in substantial drug removal and therapeutic failure 1.
For patients with residual renal function, dosing may need adjustment based on creatinine clearance using the formula: Ke = 0.0766 + 0.0060 × CrCl 2.
Metformin interaction warning: If the patient is taking metformin, cephalexin can increase metformin levels by 24-34%, requiring careful monitoring and potential metformin dose adjustment 3.
Alternative Considerations for Penicillin Allergy
If cephalexin is being used due to penicillin allergy, guidelines recommend 600 mg clindamycin orally 1 hour before procedures for hemodialysis patients requiring antibiotic prophylaxis 4.
Cross-reactivity risk exists between penicillins and cephalosporins, so true penicillin allergy should be confirmed before using cephalexin 3.