Why was cephalexin prescribed to my patient (pt)?

Cephalexin Use in Clinical Practice

Cephalexin was most likely prescribed to your patient for a skin and soft tissue infection such as cellulitis, as it is a first-line treatment for these common infections. 1

Common Indications for Cephalexin

• Cephalexin is a first-generation cephalosporin primarily used for skin and soft tissue infections, particularly cellulitis without purulence, where streptococci and methicillin-sensitive Staphylococcus aureus are the predominant pathogens 1
• It is also commonly used for uncomplicated urinary tract infections due to its high urinary concentration and effectiveness against common uropathogens 2, 3
• Cephalexin may be prescribed for upper respiratory tract infections, though it has limitations for infections caused by Haemophilus influenzae 4
• It can be used as an alternative to amoxicillin for endocarditis prophylaxis in penicillin-allergic patients (without anaphylaxis history) undergoing dental procedures 1

Antimicrobial Spectrum and Efficacy

• Cephalexin is effective against gram-positive organisms including streptococci and methicillin-sensitive Staphylococcus aureus 1, 5
• It has limited activity against gram-negative organisms and no activity against MRSA or atypical pathogens 5
• Cephalexin achieves high concentrations in urine (500-1000 μg/ml following standard doses), making it effective for urinary tract infections 6
• It is rapidly absorbed from the upper intestinal tract and distributed to tissues, though it does not penetrate the cerebrospinal fluid well 6

Dosing Considerations

• For skin and soft tissue infections, the typical adult dose is 500 mg orally four times daily 1
• For uncomplicated urinary tract infections, recent evidence suggests that 500 mg twice daily is as effective as four times daily dosing 2
• Dosage adjustment is required in patients with significant renal impairment (creatinine clearance <30 ml/min) 6
• Children may require higher doses per kilogram than adults due to greater body water turnover 6

Clinical Scenarios to Avoid Cephalexin

• Infections suspected to be caused by MRSA, as cephalexin has no activity against this pathogen 5
• Animal bite wounds, as cephalexin has poor activity against Pasteurella multocida 1
• Patients with history of anaphylaxis, angioedema, or urticaria with penicillins due to potential cross-reactivity 1
• Catheter-associated asymptomatic bacteriuria, as treatment is not recommended and may lead to antimicrobial resistance 1

Common Pitfalls and Adverse Effects

• Prescribing cephalexin for infections where it lacks coverage (MRSA, Haemophilus influenzae, atypical pathogens) 5
• Gastrointestinal side effects including nausea, vomiting, and diarrhea are most common 4
• Prolonged use may result in overgrowth of non-susceptible organisms 7
• Cephalexin may cause false-positive results for urine glucose tests using Benedict's solution, Fehling's solution, or Clinitest tablets 7

Conclusion

Without knowing your patient's specific diagnosis, cephalexin was most likely prescribed for a skin and soft tissue infection such as cellulitis, a urinary tract infection, or possibly for prophylaxis before a dental procedure in a patient with specific cardiac conditions. The choice of cephalexin suggests that the infection was likely caused by susceptible gram-positive organisms like streptococci or methicillin-sensitive Staphylococcus aureus.