Is cephalexin (a cephalosporin antibiotic) safe to use in patients with moderate impaired renal function, specifically a Glomerular Filtration Rate (GFR) of 46?

Cephalexin Use with GFR of 46 mL/min

Cephalexin can be used safely in patients with a GFR of 46 mL/min, but dose adjustment is required based on the degree of renal impairment. 1

Renal Dosing Considerations

The FDA label explicitly states that cephalexin should be administered with caution in markedly impaired renal function, with careful clinical observation and laboratory monitoring, as safe dosage may be lower than usually recommended. 1

Specific Dosing Guidance

• Dose reduction becomes necessary when creatinine clearance falls below 30 mL/min 2
• With a GFR of 46 mL/min (Stage 3a chronic kidney disease), your patient falls into the moderate renal impairment category where standard dosing can generally be used, but closer monitoring is warranted 1
• Research demonstrates that cephalexin achieves adequate urinary concentrations even in patients with impaired renal function for treating most urinary tract infections 3

Pharmacokinetic Rationale

The dosing adjustment requirement stems from cephalexin's elimination pathway:

• Cephalexin is substantially excreted by the kidney, with 70-100% of the dose appearing in urine 6-8 hours after administration 2
• The drug undergoes both glomerular filtration and active tubular secretion 4, 5
• In patients with renal tubular dysfunction, the dosage interval may need to be prolonged more than predicted by creatinine clearance alone 5

Monitoring Requirements

Close clinical observation and laboratory monitoring are essential when using cephalexin in any degree of renal impairment: 1

• Monitor renal function (serum creatinine, estimated GFR) during therapy 1
• Watch for signs of drug accumulation or adverse effects 1
• The elderly are at particular risk due to age-related decline in renal function and require careful dose selection 1

Drug Interactions in Renal Impairment

If your patient is taking metformin, exercise particular caution: 1

• Cephalexin increases metformin exposure by inhibiting tubular secretion 1
• Careful patient monitoring and metformin dose adjustment may be needed 1
• This interaction is especially relevant in patients with reduced renal function where both drugs accumulate 1

Clinical Pitfalls to Avoid

• Do not use first-generation cephalosporins like cephalexin for Lyme disease—they are ineffective despite being cephalosporins 6
• Probenecid inhibits cephalexin excretion and will increase drug levels 1
• The risk of toxic reactions increases with impaired renal function 1