What is the best initial treatment approach for a patient presenting with a staph infection, considering the possibility of Methicillin-Resistant Staphylococcus Aureus (MRSA)?

Treatment of Staphylococcus Aureus Infections

For any staph infection, immediately perform incision and drainage if an abscess is present, and obtain cultures before starting antibiotics to guide definitive therapy—this is more important than the initial antibiotic choice. 1

Initial Assessment and Source Control

The most critical first step is determining whether purulent material is present:

• Incision and drainage must be performed for all abscesses and carbuncles, regardless of whether antibiotics are given 2, 1
• Obtain Gram stain and culture of purulent drainage before initiating antibiotics to confirm MRSA and guide therapy 2, 1
• For simple abscesses or furuncles, incision and drainage alone may be adequate without antibiotics 1

Antibiotic Selection Based on Severity

Mild Outpatient Infections (Non-purulent cellulitis or post-drainage)

For methicillin-susceptible S. aureus (MSSA):

• Dicloxacillin or cephalexin for 7 days is the treatment of choice 2
• These penicillinase-resistant penicillins remain first-line for MSSA infections 3

When MRSA is suspected or confirmed:

• Trimethoprim-sulfamethoxazole (TMP-SMX) 4 mg/kg/dose twice daily is first-line for uncomplicated MRSA skin infections 1
• Doxycycline 100 mg orally twice daily is an alternative option 1
• Clindamycin 600 mg orally three times daily should only be used if local resistance rates are <10% 1

Moderate Infections (Systemic signs present)

Patients with purulent infection plus systemic signs (fever >38°C, tachycardia >90 bpm, tachypnea >24 breaths/min, or abnormal WBC count) require:

• Oral antibiotics as above PLUS close monitoring for progression 2
• Consider hospitalization if immunocompromised or failing outpatient therapy 2

Severe or Complicated Infections (Hospitalization required)

For patients requiring IV therapy:

• Vancomycin 15-20 mg/kg IV every 8-12 hours with target trough 15-20 mg/mL is first-line for hospitalized MRSA infections 1, 4
• Linezolid 600 mg IV/PO twice daily has excellent efficacy and may be superior for MRSA pneumonia 1, 5, 6
• Daptomycin 6 mg/kg IV once daily should be considered for MRSA bacteremia and right-sided endocarditis, as well as complicated skin infections 1, 6
• Ceftaroline 600 mg IV every 12 hours is a newer option with proven efficacy 1

Critical Pitfalls to Avoid

Never use beta-lactam antibiotics (penicillins, cephalosporins) for MRSA, as resistance is inherent to the definition of MRSA 1

Never use daptomycin for MRSA pneumonia—it is inactivated by pulmonary surfactant and will fail 1, 6

Failure to drain abscesses leads to treatment failure regardless of antibiotic choice 1

Always check local resistance patterns for clindamycin—only use if resistance is <10% in your area 1

Duration of Treatment

Treatment duration depends on infection type:

• 5-10 days for uncomplicated skin infections 1
• 7-14 days for complicated skin and soft tissue infections 1
• At least 2 weeks for uncomplicated bacteremia 1
• 4-6 weeks for complicated bacteremia 1
• 6 weeks for endocarditis 1

Special Considerations for Bacteremia

For MRSA bacteremia:

• Use vancomycin or daptomycin for at least 2 weeks for uncomplicated cases 1
• Obtain repeat blood cultures 2-4 days after initial positive cultures to document clearance 1
• Evaluate for endocarditis and other metastatic foci 1
• Eliminate or debride other infection sources 1

Pediatric Dosing

For children with MRSA infections:

• Vancomycin IV is first-line for severe infections 1
• Clindamycin 10-13 mg/kg IV every 6-8 hours can be used empirically if local resistance is <10%, with transition to oral if susceptible 1
• Linezolid 600 mg PO/IV twice daily for children >12 years or 10 mg/kg every 8 hours for children <12 years 1

Prevention of Recurrence

Consider decolonization only in selected cases:

• Recurrent skin infections despite optimized wound care 1
• Ongoing transmission among household contacts 1

Decolonization regimen:

• Mupirocin nasal ointment twice daily for 5-10 days 1
• Chlorhexidine body wash or dilute bleach baths for 5-14 days 1