Treatment principles for MSSA and MRSA

Treatment principles for methicillin-sensitive Staphylococcal aureus (MSSA) and methicillin resistant Staphylococcal aureus (MRSA):

• do not give systemic antibiotics to patients with minor soft skin and soft tissue infections (SSTIs) or small abscesses (<5 cm)
• incise and drain small abscesses without cellulitis and do not give antibiotic therapy
  • after incision and drainage start empirical or culture-guided systemic antibiotic therapy for larger abscesses or if there are infections in other family members
• in compromised patients or those with severe disease, give systemic antibiotic therapy based on clinical assessment and local susceptibilities of strains while awaiting definitive susceptibility results
  • ensure that empirical treatment also provides cover against S. pyogenes
    • oral flucloxacillin and clindamycin have activity against S. pyogenes, whereas tetracycline and trimethoprim often do not
• in the UK, the recommended community treatment for suspected MSSA infections is oral flucloxacillin 500-1000 mg 6 hourly (or oral clindamycin 300-450 mg 6 hourly in penicillin allergic patients); 5-7 days of treatment is normally sufficient
• if the patient is known to be MRSA-positive OR lesion cultures yield MRSA alone, then community treatment should be either oral doxycycline (contra-indicated in children <12 years) 100 mg 12 hourly, or fusidic acid 500 mg 8 hourly, or trimethoprim 200 mg 12 hourly, each combined with rifampicin 300 mg 12 hourly
  • fusidic acid and rifampicin should NOT be used as monotherapy because of the danger of resistance emergence. All these agents can be used in penicillin allergic patients
• trimethoprim (combined with sulfamethoxazole) or doxycycline without rifampicin is also effective for ambulatory therapy of MRSA SSTIs
  • oral linezolid 600 mg twice daily is an alternative option for use 'under expert guidance', but because of its high cost it should be reserved for patients who are not able to take or tolerate the above regimens
• if Group A streptococcal (GAS) infection is suspected, oral therapy should include an agent active against this organism (ß-lactam or clindamycin). For severe infections with known or suspected CA-MRSA, start treatment in hospital with parenteral vancomycin, teicoplanin, daptomycin (but not for pneumonia) or linezolid. Tigecycline may also offer broader polymicrobial cover if required. There is no evidence that one agent is superior to another
• in severe infections with features of toxic shock or necrotizing fasciitis, there is a theoretical case for using two or three agents such as linezolid combined with clindamycin and rifampicin

Notes:

• consider the possibility of CA-MRSA infection in severe community pneumonia regardless of the local prevalence of CA-MRSA

Reference:

• (1) Nathwani D et al. Guidelines for UK practice for the diagnosis and management of methicillin-resistant Staphylococcus aureus (MRSA) infections presenting in the community.J Antimicrob Chemother. 2008 May;61(5):976-94