Can Keflex (Cephalexin) be used to treat bacterial infections?

Keflex (Cephalexin) for Bacterial Infections

Keflex (cephalexin) is an effective first-line antibiotic for treating many common bacterial infections, particularly mild to moderate skin and soft tissue infections, urinary tract infections, and respiratory tract infections. 1

Indications and Effectiveness

Cephalexin is particularly effective against:

• Skin and soft tissue infections:

  • For mild non-purulent infections such as cellulitis or erysipelas, cephalexin 500mg 3-4 times daily for 5-6 days is recommended 1
  • First-line treatment for MSSA (Methicillin-Susceptible S. aureus) infections 1

• Urinary tract infections:

  • Achieves high concentrations in urine, making it effective against common urinary pathogens 2
  • Particularly effective against E. coli, Klebsiella, and Proteus mirabilis 3
  • Can be used for prophylaxis at low doses (250mg nightly) with minimal development of resistance 4

Dosing Considerations

• Standard adult dosing: 250-500mg every 6 hours (or 500mg every 12 hours in some cases) 5
• Duration: Typically 5-6 days for mild infections, longer for more severe cases 1
• Renal adjustment: Dosage reduction required in patients with creatinine clearance <30 ml/min 6
• Hemodialysis: Cephalexin is dialyzable (58% reduction after 6-hour session) 3

Antimicrobial Spectrum

Cephalexin is effective against many common bacterial pathogens but has important limitations:

• Effective against:

  • Most Gram-positive cocci (including Streptococcus and MSSA)
  • Some common Gram-negative bacteria (E. coli, Klebsiella, P. mirabilis)

• Not effective against:

  • MRSA (requires alternative agents like TMP-SMX, doxycycline, or clindamycin) 1
  • Extended-spectrum β-lactamase (ESBL) producing organisms 7
  • Pseudomonas and other resistant Gram-negative bacteria

Important Precautions

• Allergic reactions: Discontinue if allergic reaction occurs; treat with standard measures (epinephrine, antihistamines, corticosteroids) 8
• Superinfection: Prolonged use may lead to overgrowth of non-susceptible organisms 8
• Laboratory interactions: May cause false-positive results for urine glucose tests 8
• Pregnancy: Category B - no evidence of harm in animal studies, but limited human data 8

Clinical Decision Algorithm

1. Assess infection type and severity:

   • For mild-moderate skin infections, UTIs, or respiratory infections → Consider cephalexin
   • For severe infections or sepsis → Use broader spectrum antibiotics (carbapenems, etc.) 7

2. Consider local resistance patterns:

   • In areas with high MRSA prevalence → Alternative agents may be needed
   • For suspected ESBL-producing organisms → Carbapenems recommended over cephalexin 7

3. Evaluate patient factors:

   • History of anaphylactic reaction to penicillins → Avoid cephalexin
   • Renal impairment → Adjust dose accordingly
   • Pregnancy or nursing → Generally considered safe, but use only if clearly needed 8

4. Monitor response:

   • Clinical improvement expected within 72 hours
   • If no improvement, reevaluate diagnosis and consider alternative antibiotics 1

Common Pitfalls to Avoid

• Using cephalexin for MRSA infections (ineffective)
• Prescribing without a proven or strongly suspected bacterial infection (increases resistance risk) 8
• Failing to adjust dosing in patients with significant renal impairment
• Not completing the full prescribed course (may lead to treatment failure and resistance)
• Using for severe infections where broader coverage is needed (e.g., sepsis, necrotizing fasciitis)

Cephalexin remains a valuable antibiotic for common bacterial infections due to its good safety profile, reliable oral absorption, and effectiveness against many common pathogens when used appropriately.