Typical Dosing for First-Generation Cephalosporins (Cephalexin)
For adults, the standard dose of cephalexin is 250-500 mg every 6 hours orally, with a total daily dose ranging from 1-4 g divided throughout the day. 1
Adult Dosing
- For mild to moderate infections: 250 mg every 6 hours orally 1
- For more severe infections: 500 mg every 6 hours orally 1
- For streptococcal pharyngitis and uncomplicated skin infections: 500 mg every 12 hours may be sufficient 1
- For severe infections: Up to 4 g daily in divided doses 1
- If doses greater than 4 g daily are required, parenteral cephalosporins should be considered 1
Pediatric Dosing
- Standard pediatric dose: 25-50 mg/kg/day divided into 4 doses 1
- For streptococcal pharyngitis in children over 1 year: Total daily dose may be divided and administered every 12 hours 1
- For skin and skin structure infections: Total daily dose may be divided and administered every 12 hours 1
- For otitis media: Higher dosage of 75-100 mg/kg/day in 4 divided doses is recommended 1
- For β-hemolytic streptococcal infections: Treatment should continue for at least 10 days 1
Specific Clinical Scenarios
- For endocarditis (alternative therapy): Cefazolin 100 mg/kg/day IV divided every 8 hours up to 12 g daily 2
- For animal bites: Cephalexin 500 mg 3-4 times per day orally (note: misses Pasteurella multocida) 2
- For skin and soft tissue infections (MSSA): Cephalexin 500 mg 4 times per day orally 2
- For bone and joint infections in children: Recent evidence suggests 45 mg/kg (maximum 1.5 g) three times daily may be effective and well-tolerated 3
Dosing in Special Populations
- Patients with renal impairment: Dose reduction is required for patients with creatinine clearance less than 30 ml/min 4
- The reduction should be proportional to the reduced renal function 4
- Hemodialysis removes approximately 58% of cephalexin during a 6-hour session 5
Administration Considerations
- Cephalexin is administered orally and is absorbed in the upper intestine, not the stomach 4
- For oral suspension: Prepare at time of dispensing by adding appropriate amount of water 1
- After mixing, store suspension in refrigerator; stable for 14 days 1
Common Pitfalls and Caveats
- Children may require higher doses per kilogram than adults due to greater body water turnover 4
- Cephalexin does not have adequate coverage against MRSA 2
- First-generation cephalosporins have poor activity against Pasteurella multocida (common in animal bites) 2
- For streptococcal infections, a full 10-day course is necessary to prevent rheumatic fever 1
- Cephalexin should not be used in patients with immediate hypersensitivity to β-lactam antibiotics 2