What is the recommended dose of Keflex (Cephalexin) for a patient with impaired renal function?

Renal Dose Adjustment for Keflex (Cephalexin)

Patients with creatinine clearance less than 30 mL/min require a reduction in cephalexin dosage proportional to their reduced renal function, as cephalexin is 70-100% renally excreted unchanged and depends heavily on active tubular secretion. 1

Dosing Algorithm Based on Renal Function

Normal Renal Function (CrCl ≥30 mL/min)

• Standard dosing: 250-500 mg every 6-8 hours orally 1
• No dose adjustment required 1

Impaired Renal Function (CrCl <30 mL/min)

• Reduce dosage proportionally to the degree of renal impairment 1
• Determine creatinine clearance or serum creatinine before dosing 1
• Consider extending dosing interval significantly—potentially up to 20 times the normal interval in severe renal failure, as standard creatinine clearance-based adjustments substantially underestimate the required interval prolongation 2

Anephric Patients

• Single doses of 250-500 mg result in high, prolonged serum concentrations with peak levels typically within 1 hour (though delayed absorption up to 6-12 hours can occur) 3
• Hemodialysis removes approximately 58% of cephalexin over 6 hours, so supplemental dosing post-dialysis should be considered 3

Critical Considerations

The key pitfall is relying solely on creatinine clearance for dose adjustment. Cephalexin depends on active renal tubular secretion, not just glomerular filtration, and tubular function deteriorates disproportionately in renal failure 2. This means:

• Standard creatinine clearance-based nomograms significantly underestimate the required dosing interval prolongation 2
• Patients with glomerulonephritis and renal failure show substantial reduction in maximum tubular secretion transport, affecting cephalexin excretion more severely than predicted by GFR alone 2

Urinary Tract Infections in Renal Impairment

Even with impaired renal function, urinary concentrations of cephalexin remain adequate (500-1000 mcg/mL following 250-500 mg doses) for treating most urinary tract infections caused by E. coli, Klebsiella, and Proteus mirabilis 3, 1. This makes cephalexin particularly useful for UTIs in this population despite the need for dose adjustment.

Practical Approach

1. Calculate creatinine clearance (not just serum creatinine) 1
2. For CrCl <30 mL/min: Start with 250 mg and extend the interval substantially beyond what creatinine clearance alone would suggest 2
3. For dialysis patients: Dose after dialysis sessions given the 58% removal rate 3
4. Monitor clinical response, as therapeutic drug monitoring is not routinely available for cephalexin