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

Cephalexin Dosing for Patients with Creatinine Clearance of 1.5 mg/dL

For a patient with a serum creatinine of 1.5 mg/dL, the recommended dose of Keflex (cephalexin) should be reduced to 50-75% of the standard dose (250-500 mg every 8-12 hours instead of 500 mg every 6 hours) based on the estimated creatinine clearance.

Assessment of Renal Function

A serum creatinine of 1.5 mg/dL indicates moderate renal impairment, which requires dose adjustment of renally cleared medications like cephalexin. This value alone doesn't provide complete information about renal function, as other factors affect creatinine levels:

• Age (elderly patients have lower muscle mass and may have worse renal function than creatinine suggests) 1
• Body weight
• Gender
• Race

Calculating Creatinine Clearance

For proper dosing, calculate the estimated creatinine clearance using the Cockcroft-Gault formula:

CrCl = [(140 - age) × weight (kg)] / [72 × serum creatinine (mg/dL)]
(Multiply by 0.85 for females)

Cephalexin Dosing Algorithm Based on Renal Function

1. Normal renal function (CrCl >80 mL/min):

   • Standard dose: 250-500 mg every 6 hours

2. Mild to moderate renal impairment (CrCl 30-80 mL/min):

   • Dose: 250-500 mg every 8-12 hours (50-75% of standard dose)

3. Severe renal impairment (CrCl 10-30 mL/min):

   • Dose: 250-500 mg every 12-24 hours (25-50% of standard dose) 2

4. End-stage renal disease (CrCl <10 mL/min):

   • Dose: 250-500 mg every 24-48 hours
   • Consider monitoring drug levels if available

Pharmacokinetic Considerations

Cephalexin is primarily eliminated by the kidneys, with 70-100% of the dose excreted unchanged in the urine within 6-8 hours 2. In patients with impaired renal function:

• Drug clearance is reduced proportionally to the reduction in creatinine clearance
• Accumulation can occur with standard dosing
• Despite reduced clearance, urinary concentrations remain adequate for treating most urinary tract infections 3

Monitoring Recommendations

1. Monitor renal function during therapy, especially if treatment is prolonged
2. Watch for signs of drug accumulation:
   • Neurotoxicity (confusion, myoclonus)
   • Gastrointestinal effects (nausea, vomiting)

Important Clinical Considerations

• Even mild elevations in creatinine can be clinically significant and associated with adverse outcomes 4
• Elderly patients may have significantly reduced renal function despite only modest elevations in serum creatinine 1
• For patients on hemodialysis, cephalexin is significantly removed (approximately 58% reduction in serum concentration during a 6-hour session) 3

Alternative Antibiotics

If the infection is severe or the patient has very poor renal function, consider antibiotics with less renal dependence for clearance or those with established dosing protocols for renal impairment.

Remember that appropriate dose adjustment is essential to maintain efficacy while minimizing the risk of adverse effects in patients with renal impairment.