Does Keflex (cephalexin) affect a condition?

Keflex (Cephalexin) Effectiveness for Various Conditions

Cephalexin (Keflex) is ineffective against Lyme disease as it has no activity in vitro against Borrelia burgdorferi, making it an inappropriate choice for treating this infection. 1

Effectiveness by Condition

Effective for:

• Skin and Soft Tissue Infections

  • Recommended for impetigo, cellulitis, and other skin infections caused by susceptible organisms 1
  • Standard adult dosage: 250-500 mg four times daily 1
  • Pediatric dosage: 25-50 mg/kg/day in 3-4 divided doses 1
  • Effective against methicillin-susceptible Staphylococcus aureus (MSSA) skin infections 1

• Urinary Tract Infections

  • Achieves high concentrations in urine 2
  • Effective against common urinary tract pathogens 1, 2
  • Used for uncomplicated UTIs in Australia and other regions 1

• Upper Respiratory Tract Infections

  • Effective for pharyngitis and tonsillitis due to beta-hemolytic streptococci 3
  • Comparable to penicillin for streptococcal infections 3

Ineffective for:

• Lyme Disease

  • No activity against Borrelia burgdorferi 1
  • In one study, 45% of patients treated with cephalexin for Lyme disease had persistent or recurrent erythema migrans 1
  • Should not be used for Lyme disease treatment 1

• Haemophilus influenzae Infections

  • Fails in approximately 50% of otitis media cases caused by H. influenzae 3
  • Limited effectiveness in respiratory infections caused by H. influenzae 4

• Sinusitis

  • First-generation cephalosporins like cephalexin have poor coverage for H. influenzae and are therefore inappropriate for sinusitis 1

Pharmacology and Administration

• Absorption and Distribution:

  • Not absorbed from stomach but rapidly absorbed in upper intestine 5
  • Achieves therapeutic levels in serum and tissues 4
  • Rapidly cleared by kidneys with 70-100% of dose found in urine 6-8 hours after administration 5

• Dosing Considerations:

  • Children may require higher doses per kilogram than adults due to greater body water turnover 5
  • Patients with creatinine clearance <30 ml/min require dose reduction proportional to reduced renal function 5
  • Hemodialysis reduces serum concentration by approximately 58% 6

Special Considerations

• Cross-reactivity with Penicillin Allergy:

  • Cephalexin shares identical R1 side chains with amoxicillin, potentially increasing risk of cross-reactivity in patients with penicillin allergy 1
  • For patients with history of anaphylaxis to penicillins, caution is advised when considering cephalexin 1

• Cystic Fibrosis:

  • Has been studied for chronic use in cystic fibrosis patients with S. aureus infection 1
  • One small crossover trial found reduced exacerbations requiring antibiotics (25% vs 53%) and fewer hospital admissions (4% vs 22%) with cephalexin therapy 1

• Diabetic Foot Infections:

  • Recommended as empiric therapy for mild diabetic foot infections without complicating factors 1

Adverse Effects

• Generally well-tolerated with relatively infrequent adverse effects 3, 5
• Most common side effects include gastrointestinal upset, rash, and urticaria 3
• Does not disturb lower bowel flora due to absorption in upper intestine 5
• Low incidence of allergic reactions compared to some other antibiotics 5

Clinical Pitfalls

• Inappropriate use for Lyme disease can lead to treatment failure and persistent infection 1
• Not recommended for sinusitis due to poor coverage of H. influenzae 1
• Ineffective for meningitis due to poor cerebrospinal fluid penetration 4
• Should not be used prophylactically in spinal cord injured athletes with asymptomatic bacteriuria 1