At what glomerular filtration rate (GFR) is cephalexin contraindicated?

Cephalexin is NOT absolutely contraindicated at any specific GFR threshold

Cephalexin requires dose adjustment in renal impairment but does not have an absolute GFR contraindication. The FDA label states that "cephalexin should be administered with caution in the presence of markedly impaired renal function" and that "safe dosage may be lower than that usually recommended," but it does not specify a GFR cutoff where the drug becomes contraindicated 1.

Key Dosing Considerations by Renal Function

Severe Renal Impairment (GFR < 15 mL/min/1.73 m²)

• Dose adjustment is essential but the drug can still be used
• Research demonstrates that in anephric patients (GFR = 0), single doses of 250-500 mg cephalexin resulted in high, prolonged serum concentrations with peak levels within 1 hour, though absorption may be delayed in some patients 2
• The elimination half-life increases dramatically from approximately 1 hour in normal renal function to 15.4 hours in anephric patients 3

Moderate Renal Impairment (GFR 15-60 mL/min/1.73 m²)

• Dosage interval prolongation is required based on creatinine clearance
• Studies suggest the dosage interval may need to be prolonged up to 20 times normal in severe renal failure, far more than the 5-fold adjustment suggested by creatinine clearance alone 4
• At GFR approaching 0, the theoretical serum half-life reaches 8.47 hours 5

Clinical Algorithm for Use

Step 1: Assess baseline renal function (GFR/CrCl)

Step 2: Calculate appropriate dosing:

• Normal renal function (GFR ≥ 60): Standard dosing
• Mild-moderate impairment (GFR 30-60): Reduce dose or extend interval moderately
• Severe impairment (GFR < 30): Significantly extend dosing interval (up to 20x normal)
• Anephric/dialysis patients: Can still use with appropriate interval adjustment; hemodialysis removes approximately 58% of serum cephalexin over 6 hours 2

Step 3: Monitor closely with laboratory studies as recommended by FDA label 1

Important Caveats

• The drug is over 90% renally excreted unchanged, making dose adjustment critical 1
• Both glomerular filtration AND tubular secretion affect elimination, so creatinine clearance alone may underestimate the need for dose adjustment 4
• The only absolute contraindication listed is known allergy to cephalosporins 1
• Elderly patients warrant particular caution due to age-related decline in renal function 1