What is the recommended oral dose of cephalexin for an adult patient with impaired renal function?

Cephalexin Dosing in Renal Impairment

In adult patients with impaired renal function, cephalexin requires dose reduction proportional to the degree of renal impairment, specifically when creatinine clearance falls below 30 mL/min, with dosing adjustments based on creatinine clearance or serum creatinine levels. 1

Standard Dosing in Normal Renal Function

• Adults with normal renal function typically receive 250-500 mg orally every 6-8 hours, with cephalexin being rapidly and completely absorbed from the upper intestine 1
• Peak serum levels of approximately 12 mcg/mL occur 2 hours after a 500 mg oral dose in patients with normal kidney function 2
• The drug achieves urinary concentrations of 500-1000 mcg/mL following 250-500 mg doses, far exceeding minimum inhibitory concentrations for common urinary pathogens 1

Dose Adjustment Algorithm for Renal Impairment

When creatinine clearance is less than 30 mL/min, reduce the cephalexin dose proportionally to the reduced renal function. 1

Specific Adjustments Based on Renal Function:

• Mild to moderate impairment (CrCl 30-60 mL/min): Standard doses may be used with careful monitoring, though some prolongation of dosing interval may be considered 1
• Severe impairment (CrCl <30 mL/min): Significant dose reduction or interval prolongation is required, as elimination half-life increases from approximately 1 hour in normal subjects to 8.47 hours in anephric patients 2
• Anephric patients: Single doses of 250-500 mg result in high, prolonged serum concentrations with peak levels sometimes delayed up to 6-12 hours due to altered absorption 3

Critical Pharmacokinetic Considerations

• The serum half-life of cephalexin increases dramatically with declining renal function, correlating directly with creatinine clearance (Ke = 0.0766 + 0.0060 × CrCl) 2
• Renal tubular secretion is substantially diminished in renal failure, affecting cephalexin excretion more than predicted by creatinine clearance alone 4
• Dosage interval prolongation may need to be up to 20 times longer than in normal subjects, rather than the 5-fold increase suggested by creatinine clearance calculations alone 4
• Between 70-100% of the dose is normally excreted unchanged in urine within 6-8 hours, but this is markedly reduced in renal impairment 1

Hemodialysis Patients

• Hemodialysis removes cephalexin moderately, reducing serum concentrations by approximately 58% during a 6-hour dialysis session 3
• Administer supplemental doses after dialysis to maintain therapeutic levels 3
• Monitor for delayed absorption patterns, as peak levels may occur 6-12 hours post-dose in some anephric patients 3

Monitoring Parameters

• Establish baseline renal function using creatinine clearance or serum creatinine before initiating therapy 1
• In patients with borderline renal function, obtain 24-hour urine collection for more accurate assessment of renal impairment 5
• Adjust dosing based on individual patient response and renal function trends 2

Important Clinical Caveats

• First-generation cephalosporins like cephalexin are inactive against Borrelia burgdorferi and should never be used for Lyme disease 5
• Cephalexin does not penetrate into cerebrospinal fluid or aqueous humor, limiting its use in CNS or ocular infections 1
• The drug has low protein binding and undergoes no metabolism, with elimination entirely dependent on renal excretion 1
• Unlike doxycycline or azithromycin, which require no dose adjustment in renal impairment, cephalexin necessitates careful dosing modifications 6, 7