Keflex (Cephalexin) Dosing Guidelines in Chronic Renal Failure
Keflex (cephalexin) dosage must be reduced in patients with chronic renal failure, with specific adjustments based on creatinine clearance levels. 1
Dosing Algorithm Based on Renal Function
Normal Renal Function
- Standard adult dosing: 250-500 mg orally every 6 hours (1-2 g/day)
Impaired Renal Function
- Creatinine clearance 30-50 ml/min: No dosage adjustment needed
- Creatinine clearance 10-30 ml/min: 250-500 mg every 8-12 hours
- Creatinine clearance <10 ml/min: 250-500 mg every 12-24 hours
- Hemodialysis patients: 250-500 mg every 24 hours, with supplemental dose after dialysis
Pharmacokinetic Considerations
Cephalexin is primarily eliminated through renal excretion, with 70-100% of the dose found in urine within 6-8 hours after administration in patients with normal renal function 2. In patients with renal impairment:
- Serum half-life increases significantly from approximately 1 hour in normal subjects to 6-18 hours in severe renal impairment 3
- Drug accumulation occurs when standard dosing is used in renal failure
- Hemodialysis removes approximately 58% of cephalexin during a 6-hour session 4
Monitoring Recommendations
- Check baseline renal function (BUN, creatinine) before initiating therapy
- Monitor renal function during treatment, especially in patients with markedly impaired renal function
- Assess for signs of drug toxicity (neurotoxicity, seizures) that may occur with drug accumulation
- Monitor for superinfection, particularly in patients on prolonged therapy
Important Clinical Considerations
- Despite reduced clearance, cephalexin still achieves adequate urinary concentrations for treating most urinary tract infections even in patients with impaired renal function 4
- Careful clinical observation and laboratory monitoring are essential in patients with markedly impaired renal function 1
- In anephric patients, absorption may be delayed, with peak levels sometimes occurring 6-12 hours after administration rather than the typical 1 hour 4
Potential Complications and Management
- Watch for positive direct Coombs' tests, which may occur during treatment with cephalosporins 1
- Monitor for superinfection with non-susceptible organisms during prolonged therapy
- Be alert for allergic reactions, which require immediate discontinuation and appropriate treatment
- Consider potential fall in prothrombin activity, especially in patients with renal impairment 1
The CLCR-PSP15' method (combining creatinine clearance and phenolsulfonphthalein test) has been shown to provide better control of plasma cephalexin concentrations in patients with renal impairment compared to using creatinine clearance alone 5, but in clinical practice, the creatinine clearance-based dosing approach remains the standard method for dose adjustment.