What is the recommended dosing for Keflex (Cephalexin) in a typical adult patient with a mild to moderate bacterial infection and potential Impaired renal function?

Keflex (Cephalexin) Dosing for Adults

For typical adult patients with mild to moderate bacterial infections and normal renal function, the standard dose of Keflex is 250 mg every 6 hours or 500 mg every 12 hours, with a maximum daily dose of 4 grams. 1

Standard Adult Dosing

• Mild to moderate infections: 250 mg every 6 hours (four times daily) 1
• Alternative regimen for specific infections: 500 mg every 12 hours for streptococcal pharyngitis, skin and soft tissue infections, and uncomplicated cystitis 1
• More severe infections: Higher doses may be required, but total daily dose should remain within 1-4 grams 1
• Streptococcal infections: Continue treatment for at least 10 days 1

The IDSA guidelines support cephalexin at 500 mg four times daily for adults with methicillin-susceptible Staphylococcus aureus infections, which aligns with the FDA-approved dosing 2, 3

Dosing Adjustments for Impaired Renal Function

Patients with creatinine clearance less than 30 mL/min require dose reduction proportional to their reduced renal function. 4

Specific Renal Dosing Recommendations

• Creatinine clearance <30 mL/min: Reduce dosage proportionally based on degree of renal impairment 4
• Hemodialysis patients: Administer standard dose after dialysis sessions, as hemodialysis removes approximately 58% of cephalexin over 6 hours 5
• Monitoring: Establish baseline renal function via creatinine clearance or serum creatinine before adjusting doses 4

Even in patients with severely impaired renal function, cephalexin achieves adequate urinary concentrations (500-1000 mcg/mL) for treating most urinary tract infections after standard 250-500 mg doses 4. However, serum levels become elevated and prolonged in anephric patients, necessitating dose reduction 5.

Critical Clinical Considerations

Microbiological Coverage Limitations

• Effective against: Methicillin-susceptible Staphylococcus aureus, Streptococcus species, E. coli, Klebsiella, and Proteus mirabilis 3, 5
• NOT effective against: MRSA, Pasteurella multocida, and most anaerobes 3

If MRSA is suspected, cephalexin is inadequate and alternative agents (trimethoprim-sulfamethoxazole, doxycycline, or clindamycin) must be used instead. 3

Allergy Considerations

• Penicillin allergy: Patients with immediate hypersensitivity reactions to penicillin should avoid cephalexin due to potential cross-reactivity (2-4% risk) 3, 6
• Non-immediate reactions: Cephalexin remains an appropriate alternative 3

Common Pitfalls to Avoid

• Inadequate duration: For β-hemolytic streptococcal infections, therapeutic dosing must continue for at least 10 days to prevent complications 1
• Delayed absorption: In some patients (particularly those with renal failure), peak levels may be delayed up to 6-12 hours rather than the typical 1 hour 5
• Exceeding maximum dose: If daily doses greater than 4 grams are required, parenteral cephalosporins should be considered instead 1