What antibiotic is indicated for a patient with cellulitis and fever?

Antibiotic Treatment for Cellulitis with Fever and Red Streaks

Cephalexin (option B) is the most appropriate antibiotic for a patient with cellulitis on the lateral leg with red streaks and fever, as it provides excellent coverage against the most common causative organisms (streptococci and staphylococci) while being suitable for outpatient management. 1

Pathophysiology and Clinical Assessment

Cellulitis with red streaks (lymphangitis) and fever represents a moderate to severe soft tissue infection that requires prompt antibiotic therapy. The clinical presentation suggests:

• Active infection spreading through lymphatic vessels (red streaks)
• Systemic involvement (fever)
• Likely causative organisms: beta-hemolytic streptococci and Staphylococcus aureus

First-Line Antibiotic Selection

For typical cellulitis, therapy should target streptococci as the primary pathogen:

• Cephalexin (500 mg orally every 6 hours) is recommended by the Infectious Diseases Society of America (IDSA) as a first-line agent for cellulitis 1
• It provides excellent coverage against streptococci and methicillin-sensitive Staphylococcus aureus (MSSA)
• The presence of fever doesn't necessarily require IV antibiotics if the patient is otherwise stable and can tolerate oral medication

Why Not the Other Options?

1. Penicillin (option A): While active against streptococci, it has limited activity against S. aureus, which is a potential pathogen in cellulitis 1

2. Erythromycin (option C): Not recommended as first-line therapy due to increasing resistance rates among streptococci and staphylococci 1

3. Ceftriaxone (option D): While effective, this is an IV antibiotic that would be reserved for:

   • Patients requiring hospitalization
   • More severe infections
   • Patients unable to take oral medications 1

Special Considerations

MRSA Coverage

• MRSA is an unusual cause of typical cellulitis
• A prospective study demonstrated that treatment with beta-lactams like cefazolin or oxacillin was successful in 96% of cellulitis cases 1
• However, if there are risk factors for MRSA (prior MRSA infection, purulent drainage, penetrating trauma, injection drug use), consider adding MRSA coverage 1

Duration of Therapy

• A 5-day course of antimicrobial therapy is as effective as a 10-day course if clinical improvement occurs by day 5 1

Adjunctive Measures

• Elevation of the affected area to promote gravity drainage of edema and inflammatory substances 1
• Systemic corticosteroids could be considered in non-diabetic adult patients with cellulitis to reduce inflammation 1

Treatment Algorithm

1. For typical cellulitis with fever but without purulence or abscess:

   • Cephalexin 500 mg orally four times daily for 5-10 days

2. If patient has risk factors for MRSA or fails to respond to initial therapy:

   • Consider adding coverage for MRSA (clindamycin, TMP-SMX, or doxycycline)

3. If patient has severe infection requiring hospitalization:

   • Switch to IV antibiotics (cefazolin, oxacillin, or ceftriaxone)

4. For patients with true penicillin allergy:

   • Clindamycin 300-450 mg orally four times daily

Remember that blood cultures are unnecessary for typical cases of cellulitis but should be obtained for patients with malignancy, severe systemic features, or unusual predisposing factors 1.