What is the dosing for Keflex (cephalexin)?

Cephalexin Dosing Guidelines

For adults with skin and soft tissue infections, the standard oral dose of cephalexin is 500 mg three to four times daily, while for children the recommended dosage is 25-50 mg/kg/day divided into 3-4 doses. 1, 2

Adult Dosing

• Standard adult dose: 250 mg every 6 hours 1
• For skin and soft tissue infections: 500 mg every 8 hours or 500 mg every 6 hours (3-4 times daily) 2, 1
• For streptococcal pharyngitis and uncomplicated cystitis: 500 mg every 12 hours 1
• Total daily dose should be within 1-4 grams per day 1
• Duration of therapy for skin infections is typically 7 days, depending on clinical response 2

Pediatric Dosing

• Standard pediatric dose: 25-50 mg/kg/day divided into 3-4 doses 1
• For streptococcal pharyngitis and skin infections in children over 1 year: total daily dose may be divided and administered every 12 hours 1
• For otitis media: 75-100 mg/kg/day in 4 divided doses 1
• For β-hemolytic streptococcal infections: treatment should continue for at least 10 days 1
• For methicillin-susceptible Staphylococcus aureus (MSSA) infections: 25 mg/kg/day in 4 divided doses 3

Specific Clinical Scenarios

Skin and Soft Tissue Infections

• For methicillin-susceptible S. aureus (MSSA) skin infections: 500 mg four times per day for adults 3
• For pediatric MSSA skin infections: 25 mg/kg/day in 4 divided doses 3
• For impetigo: 250 mg four times per day for adults; 25 mg/kg/day in 4 divided doses for children 3

Urinary Tract Infections

• Recent evidence suggests twice-daily dosing (500 mg BID) is as effective as four-times-daily dosing for uncomplicated UTIs in women 4
• For cystitis: therapy should be continued for 7-14 days 1

Pneumonia

• For oral therapy of methicillin-susceptible S. aureus pneumonia: 75-100 mg/kg/day in 3-4 doses for children 3

Dosing in Special Populations

• For patients with renal impairment (creatinine clearance <30 ml/min): dose reduction proportional to reduced kidney function is required 5
• Hemodialysis reduces serum concentration of cephalexin by approximately 58% during a 6-hour session 6

Clinical Considerations

• Cephalexin is effective against common skin pathogens including Staphylococcus aureus (except MRSA) and Streptococcus species 2
• Cephalexin is not effective against MRSA; alternative agents should be considered if MRSA is suspected 2
• Cephalexin is rapidly absorbed from the upper intestinal tract and achieves high concentrations in urine 5
• For severe infections or those caused by less susceptible organisms, larger doses may be needed 1
• If daily doses greater than 4g are required, parenteral cephalosporins should be considered 1

Potential Pitfalls

• Cephalexin has limited activity against Pasteurella multocida and anaerobes 2
• Children may require higher doses per kilogram than adults due to greater body water turnover 5
• Cephalexin does not penetrate the cerebrospinal fluid well and should not be used for central nervous system infections 5
• For long-term suppressive therapy of recurrent UTIs, lower doses (125-250 mg daily) have been used successfully in elderly patients 7