What is the recommended dosing for Keflex (cefalexin)?

Cephalexin (Keflex) Dosing Recommendations

The standard adult dosage of cephalexin ranges from 1 to 4 g daily in divided doses, with the usual adult dose being 250 mg every 6 hours or 500 mg every 12 hours for most common infections. 1

Adult Dosing

• For most infections, adults should receive 250 mg every 6 hours (1 g daily) 1
• For streptococcal pharyngitis, skin and skin structure infections, and uncomplicated cystitis in patients over 15 years of age, 500 mg every 12 hours is recommended 1
• For more severe infections, the dose may be increased to 500 mg four times daily (2 g daily) 2
• For skin and soft tissue infections specifically, 500 mg three times daily for 7 days is an effective regimen 2, 3
• If daily doses greater than 4 g are required, parenteral cephalosporins should be considered 1

Pediatric Dosing

• The usual recommended daily dosage for pediatric patients is 25 to 50 mg/kg divided into 4 doses 1
• For streptococcal pharyngitis in patients over 1 year of age and for skin and skin structure infections, the total daily dose may be divided and administered every 12 hours 1
• For otitis media, clinical studies have shown that a higher dosage of 75 to 100 mg/kg/day in 4 divided doses is required 1
• In severe infections, the pediatric dosage may be doubled 1

Duration of Therapy

• For most uncomplicated infections, 7 days of therapy is typically sufficient 2
• For β-hemolytic streptococcal infections, a therapeutic dosage should be administered for at least 10 days 1
• For uncomplicated cystitis, therapy should be continued for 7 to 14 days 1
• If the infection has not improved within 5 days, treatment should be extended or reconsidered 2

Special Considerations

• Patients with renal impairment (creatinine clearance less than 30 ml/min) require a reduction in cephalexin dosage proportional to the reduced kidney function 4
• Cephalexin is not effective against MRSA; if MRSA is suspected or confirmed, alternative agents should be considered 2
• Cephalexin has good activity against staphylococci and streptococci but limited activity against anaerobes 2
• Recent research suggests that twice-daily dosing (500 mg BID) is as effective as four-times-daily dosing for uncomplicated urinary tract infections, which may improve patient adherence 5

Clinical Pearls

• Cephalexin is rapidly absorbed in the upper intestine and achieves high urinary concentrations (500-1000 μg/ml) following 250-500 mg oral doses 4
• For prophylaxis of recurrent urinary tract infections, low-dose therapy (250 mg nightly) has been shown to be effective without promoting antimicrobial resistance 6
• Cephalexin can be administered in relatively high oral doses without gastrointestinal irritation 4
• For simple skin abrasions without signs of significant infection, topical antimicrobial agents may be sufficient instead of systemic cephalexin 2

Common Pitfalls

• Avoid using cephalexin for suspected MRSA infections, as it is not effective against this pathogen 2
• Do not use cephalexin for the treatment of Lyme disease, as it is ineffective for this condition 3
• Be cautious in patients with a history of immediate hypersensitivity to penicillin, as there may be cross-reactivity with cephalosporins 7
• Remember to adjust dosing in patients with significant renal impairment 4