What are the uses and dosages of Cephalexin (Cefalexin), a cephalosporin (antibiotic)?

Cephalexin Uses and Dosages

Cephalexin is a first-generation cephalosporin antibiotic primarily used to treat skin and soft tissue infections, urinary tract infections, respiratory tract infections, and otitis media, with dosing ranging from 250-500 mg four times daily for adults and 25-50 mg/kg/day in divided doses for children.

Indications for Use

Skin and Soft Tissue Infections

• Uncomplicated cellulitis: First-line empiric treatment targeting streptococci and methicillin-sensitive staphylococci 1
• Impetigo: Effective against Staphylococcus aureus and Streptococcus pyogenes 2
• Skin structure infections: Recommended for mild to moderate infections 2

Urinary Tract Infections

• Uncomplicated cystitis: Effective for patients over 15 years of age 3
• UTIs in children: Recommended for children older than 28 days 2
• Febrile UTIs: Oral option after initial parenteral therapy 2

Respiratory Tract Infections

• Streptococcal pharyngitis: Effective alternative to penicillin 3, 4
• Otitis media: Requires higher dosing (75-100 mg/kg/day) for effectiveness 3, 4
• Upper respiratory infections: Effective except for those caused by Haemophilus influenzae 4
• Lower respiratory infections: Effective for most community-acquired infections except those caused by H. influenzae 5

Dosage Recommendations

Adult Dosing

• General range: 1-4 g daily in divided doses 3
• Standard dosing: 250 mg every 6 hours (four times daily) 3
• Skin and soft tissue infections: 500 mg four times daily 2
• Streptococcal pharyngitis: 500 mg every 12 hours 3
• Uncomplicated cystitis: 500 mg every 12 hours for 7-14 days 3
• Uncomplicated UTIs: Recent evidence suggests 500 mg twice daily is as effective as four times daily dosing 6

Pediatric Dosing

• General range: 25-50 mg/kg/day in divided doses 3
• Streptococcal pharyngitis: Total daily dose may be divided and administered every 12 hours 3
• Skin infections: Total daily dose may be divided and administered every 12 hours 3
• Otitis media: Higher dosage of 75-100 mg/kg/day in 4 divided doses 3
• UTIs in children 29-60 days old: 50-100 mg/kg/day in 4 divided doses 2
• β-hemolytic streptococcal infections: Treatment should continue for at least 10 days 3

Special Considerations

Renal Impairment

• Dose adjustment required for patients with creatinine clearance less than 30 ml/min 7
• Reduction should be proportional to the reduced kidney function 7

Duration of Therapy

• Uncomplicated skin/soft tissue infections: 5-7 days 1
• Streptococcal infections: At least 10 days to prevent rheumatic fever 3
• Urinary tract infections: 7-14 days 3

Advantages and Limitations

• Advantages:

  • Well-absorbed from the gastrointestinal tract 7
  • Achieves high concentrations in urine 8
  • Low incidence of side effects 7, 4
  • Available as oral suspension for pediatric use 3

• Limitations:

  • Not effective against Haemophilus influenzae 4, 5
  • Does not achieve adequate cerebrospinal fluid levels 5
  • May not be effective against MRSA without additional coverage 2

Monitoring and Follow-up

• Reevaluate patients with skin infections in 48-72 hours to assess response 1
• Consider hospitalization if no improvement within 24-48 hours of outpatient treatment 1
• Monitor for adverse effects, primarily gastrointestinal upset, rash, and urticaria 4

Practical Administration Tips

• Oral suspension preparation instructions:
  • For 125 mg/5 mL (100 mL): Add 71 mL water
  • For 250 mg/5 mL (100 mL): Add 71 mL water
  • After mixing, store in refrigerator for up to 14 days 3

Cephalexin remains a valuable antibiotic with broad clinical applications due to its efficacy against common pathogens, favorable safety profile, and convenient oral administration.