What is the recommended oral cephalosporin (first-generation cephalosporin) dosage for treating common bacterial infections?

Recommended Oral Cephalosporin Dosages for Common Bacterial Infections

For treating common bacterial infections, the recommended first-generation oral cephalosporin dosage is cephalexin 500 mg three to four times daily for adults and 25-50 mg/kg/day divided into 3-4 doses for children. 1, 2

Adult Dosing Recommendations

First-Generation Cephalosporins

• Cephalexin (Keflex)
  • Standard dose: 500 mg orally 3-4 times daily 1
  • Severe infections: Up to 4 g daily in divided doses 2
  • Duration: 5-7 days for most infections; 10 days for streptococcal pharyngitis 1, 3

Second-Generation Cephalosporins

• Cefaclor
  • Standard dose: 250 mg orally every 8 hours 4
  • Severe infections: 500 mg orally every 8 hours 4
  • Maximum: 1 g daily 4

Pediatric Dosing Recommendations

First-Generation Cephalosporins

• Cephalexin
  • Standard dose: 25-50 mg/kg/day divided into 3-4 doses 2
  • Severe infections: Up to 100 mg/kg/day divided into 4 doses 2

Second-Generation Cephalosporins

• Cefaclor
  • Standard dose: 20 mg/kg/day divided every 8 hours 4
  • Otitis media/severe infections: 40 mg/kg/day divided every 8 hours 4, 5
  • Maximum: 1 g daily 4
  • Alternative B.I.D. dosing for pharyngitis and otitis media available 4

Infection-Specific Recommendations

Skin and Soft Tissue Infections

• First-line: Cephalexin 500 mg 3-4 times daily for 5-6 days 1, 3
• Clinical cure rates of 89% have been demonstrated for uncomplicated skin infections 6

Respiratory Tract Infections

• Pharyngitis/Tonsillitis: Cephalexin 500 mg 3-4 times daily for 10 days 2
• Otitis Media:
  • Cephalexin 50-100 mg/kg/day divided into 3-4 doses 2
  • Note: May be less effective against H. influenzae (50% failure rate) 2
  • Consider cefaclor 40 mg/kg/day for better H. influenzae coverage 7, 5

Urinary Tract Infections

• Cephalexin 500 mg 3-4 times daily for 7-14 days 2

Clinical Considerations

Advantages of Oral Cephalosporins

• Good absorption profile (85-90% bioavailability for cephalexin) 8
• Relatively short half-life (1-2 hours) requiring multiple daily doses 8
• Primary elimination through kidneys 8

Common Pitfalls to Avoid

1. Inadequate dosing for H. influenzae infections: First-generation cephalosporins have limited activity against H. influenzae; consider second-generation options like cefaclor for these infections 2, 7
2. Insufficient duration for streptococcal infections: Treat beta-hemolytic streptococcal infections for at least 10 days to prevent complications 4
3. Failure to adjust for renal impairment: While cefaclor generally doesn't require dose adjustment in renal impairment, other cephalosporins may need adjustment 4
4. Inappropriate MRSA coverage: Standard oral cephalosporins lack reliable activity against MRSA; consider alternative agents if MRSA is suspected 1, 6

Adverse Effects

• Generally well-tolerated with infrequent adverse effects 2
• Most common side effects: gastrointestinal upset, rash, and urticaria 2
• Diarrhea more common with cefaclor (10%) than cephalexin (4%) 6

When selecting an oral cephalosporin, consider the specific pathogen, infection site, local resistance patterns, and patient factors such as age, renal function, and medication allergies.