What is the recommended treatment for a skin infection over the knee in a patient with no known allergies to penicillin or cephalosporins?

Treatment of Skin Infection Over the Knee

For a skin infection over the knee in a patient without penicillin or cephalosporin allergies, treat with oral cephalexin 500 mg three to four times daily for 7-10 days, or alternatively, a penicillinase-resistant penicillin such as dicloxacillin 500 mg four times daily for the same duration. 1

First-Line Antibiotic Selection

Primary Treatment Options

• Cephalexin (first-generation cephalosporin) is highly effective for streptococcal and staphylococcal skin infections, with cure rates of 90% or higher. 2
• Penicillinase-resistant semisynthetic penicillins (dicloxacillin, flucloxacillin) or first-generation cephalosporins (cephalexin, cefazolin) should be selected for cellulitis and most skin infections. 1
• These agents provide excellent coverage against Staphylococcus aureus and Streptococcus pyogenes, the two most common pathogens in skin and soft tissue infections. 1, 3

Dosing Regimens

• Cephalexin: 500 mg orally three to four times daily for 7-10 days 1, 2
• Dicloxacillin: 500 mg orally four times daily for 7-10 days 1
• Flucloxacillin: 500 mg orally four times daily for 7-10 days 3

Alternative Options for Improved Compliance

Second-Generation Cephalosporins

• Cefprozil offers equivalent clinical efficacy to cephalexin but with more convenient once or twice-daily dosing, which may improve patient compliance. 4
• Cefadroxil and cefprozil can be given once daily with better tolerability profiles, though they are more expensive than cephalexin. 5

When to Consider Broader Coverage

• If the infection does not respond to initial empirical therapy directed against S. aureus and S. pyogenes, obtain appropriate culture material to guide further treatment. 1
• For infections associated with trauma, water contact, or animal/insect bites, broader antimicrobial coverage may be necessary. 1

Important Clinical Considerations

Duration of Therapy

• Although antibiotics have been given for 10 days in most clinical trials, there is no evidence that this duration is more effective than a 7-day course. 5
• The IDSA guidelines recommend 7-10 days for most uncomplicated skin infections. 1

Monitoring for Treatment Failure

• Patients who do not respond to initial therapy should have cultures obtained to identify resistant organisms, including methicillin-resistant S. aureus (MRSA). 1
• For community-acquired MRSA infections in otherwise healthy patients, clindamycin or trimethoprim-sulfamethoxazole are appropriate oral alternatives. 3, 5

Common Pitfalls to Avoid

• Do not use cephalexin for infections involving the auricle (ear cartilage), as it lacks adequate Pseudomonas aeruginosa coverage. 6
• Avoid using vancomycin, teicoplanin, or daptomycin for erysipeloid infections, as Erysipelothrix rhusiopathiae is resistant to these agents. 1
• Ensure the infection is not necrotizing fasciitis or gas gangrene, which require immediate surgical intervention and different antimicrobial regimens (clindamycin plus penicillin). 1

When Parenteral Therapy Is Needed

• For severe infections requiring intravenous therapy, ceftriaxone 1 g every 12 hours offers the advantage of once-daily dosing and may be suitable for outpatient treatment. 5
• Cefazolin 1 g every 8 hours or ampicillin-sulbactam 1.5-3.0 g every 6 hours are also effective parenteral options. 1