What is the dosage and treatment duration of Cephalexin (Cefalexin) for bacterial infections?

Cephalexin Dosage and Treatment Duration for Bacterial Infections

For bacterial infections, cephalexin is typically dosed at 250-500 mg orally every 6 hours for adults (total daily dose 1-4g), with treatment duration ranging from 5-14 days depending on the infection type. 1

Adult Dosing Guidelines

Standard Adult Dosing:

• Standard dose: 250 mg every 6 hours (1g daily) 1
• Higher dose option: 500 mg every 12 hours (1g daily) for: 1
  • Streptococcal pharyngitis
  • Skin and skin structure infections
  • Uncomplicated cystitis in patients over 15 years

Infection-Specific Dosing:

• Skin/soft tissue infections: 500 mg every 6 hours or 500 mg every 12 hours for 5-6 days 2
• Urinary tract infections: 500 mg every 12 hours for 7-14 days 1
• More severe infections: May require up to 4g daily in divided doses 1

Important Considerations:

• For infections requiring >4g daily, consider parenteral cephalosporins 1
• Cephalexin is rapidly absorbed in the upper intestine and doesn't disturb lower bowel flora 3
• 70-100% of the dose is excreted in urine within 6-8 hours 3

Pediatric Dosing Guidelines

Standard Pediatric Dosing:

• Usual daily dose: 25-50 mg/kg/day divided into 4 doses 1
• Severe infections: May double the dosage 1
• Otitis media: 75-100 mg/kg/day in 4 divided doses 1

Alternative Dosing Schedules:

• For streptococcal pharyngitis and skin/skin structure infections in children >1 year: total daily dose may be divided and administered every 12 hours 1
• Recent research supports twice-daily (BID) dosing for MSSA infections: 4
  • 22-45 mg/kg BID for MIC 1-2 mg/L
  • 80 mg/kg BID for MIC 4 mg/L

Treatment Duration

• Streptococcal infections: Minimum 10 days 1
• Skin/soft tissue infections: 5-6 days 2
• Urinary tract infections: 7-14 days 1
• Chronic UTIs: 10 days (based on older studies) 5

Special Populations

Renal Impairment:

• Patients with creatinine clearance <30 mL/min require dose reduction proportional to reduced kidney function 3
• Dose adjustment can be based on creatinine clearance or serum creatinine levels 3

Clinical Pearls

• Cephalexin suspension must be prepared at time of dispensing and can be kept refrigerated for 14 days without significant potency loss 1
• Twice-daily dosing (500 mg BID) has been shown to be as effective as four-times-daily dosing for UTIs, which may improve adherence 5
• Cephalexin is one of several recommended options for skin and soft tissue infections per IDSA guidelines 6
• For surgical site infections of the trunk or extremities (away from axilla or perineum), cephalexin 500 mg every 6 hours orally is an appropriate option 6

Common Pitfalls to Avoid

• Failing to adjust dosing in patients with significant renal impairment
• Insufficient treatment duration for streptococcal infections (should be minimum 10 days)
• Using cephalexin for suspected MRSA infections (it's not effective against MRSA)
• Not considering twice-daily dosing regimens when adherence is a concern

When prescribing cephalexin, always consider the site and severity of infection, likely pathogens, patient factors (including renal function), and the need to optimize adherence through appropriate dosing frequency.