Renal Dosing for Keflex (Cephalexin)
For patients with creatinine clearance less than 30 mL/min, reduce the cephalexin dose proportionally to the degree of renal impairment, typically requiring dose reduction or interval extension to prevent drug accumulation. 1
Dosing Algorithm Based on Renal Function
Normal to Mild Renal Impairment (CrCl >30 mL/min)
- Use standard dosing without adjustment (250-500 mg every 6-8 hours) 1
- No modification needed as urinary concentrations remain adequate for most urinary tract pathogens 2
Moderate to Severe Renal Impairment (CrCl <30 mL/min)
- Reduce dosage proportionally to the reduced creatinine clearance 1
- The serum half-life increases significantly from 1 hour in normal patients to approximately 8.5 hours in anephric patients 3
- A practical approach: 250 mg every 8-12 hours maintains therapeutic levels while minimizing accumulation 4
End-Stage Renal Disease and Hemodialysis
- In anephric patients, single doses of 250-500 mg result in high, prolonged serum concentrations with peak levels typically within 1 hour 2
- Hemodialysis removes approximately 58% of cephalexin over a 6-hour session 2
- Administer doses after hemodialysis sessions to avoid premature drug removal 2
- Consider 250-500 mg post-dialysis, with subsequent doses every 12-24 hours depending on residual renal function 3
Pharmacokinetic Considerations
The elimination rate constant (Ke) correlates directly with creatinine clearance: Ke = 0.0766 + 0.0060 × CrCl 3. This relationship allows precise calculation of individualized dosing intervals based on measured creatinine clearance.
Key Absorption Characteristics
- Cephalexin is completely absorbed from the upper intestine (not the stomach) 1
- Peak serum levels occur at 1-2 hours post-dose in most patients 2, 3
- However, delayed absorption can occur—in 2 of 6 anephric patients, peak levels were delayed to 6-12 hours 2
Important Clinical Caveats
Urinary Tract Infections in Renal Impairment
- Even with impaired renal function, urinary concentrations of cephalexin remain adequate (500-1000 mcg/mL) for treating most UTIs caused by E. coli, Klebsiella, and Proteus mirabilis 2, 1
- This makes cephalexin particularly useful for UTI treatment even in moderate renal dysfunction 2
Monitoring Parameters
- Determine creatinine clearance or serum creatinine before initiating therapy in patients with suspected renal impairment 1
- For borderline renal function, consider 24-hour urine collection for accurate assessment (similar principles apply as with other renally-cleared antibiotics) 5
- Watch for delayed absorption patterns in anephric patients, which can affect timing of peak concentrations 2
Dosing Pitfalls to Avoid
- Do not use standard dosing intervals in patients with CrCl <30 mL/min, as this leads to significant drug accumulation 3
- The conventional creatinine clearance method alone may be insufficient for drugs with significant tubular secretion like cephalexin—consider both glomerular and tubular function when available 6
- Children may require higher per-kilogram doses than adults due to greater body water turnover 1