What is the best treatment regimen for a patient with Methicillin-resistant Staphylococcus aureus (MRSA) and Acinetobacter baumannii infections?

From the Guidelines

The best treatment regimen for a patient with both MRSA and Acinetobacter baumannii infections typically involves combination antimicrobial therapy, with intravenous vancomycin (15-20 mg/kg every 8-12 hours, adjusted based on trough levels of 15-20 μg/mL) or daptomycin (6-10 mg/kg once daily) for MRSA, and a carbapenem such as meropenem (1 g every 8 hours) combined with colistin (loading dose of 9 million units, then 4.5 million units every 12 hours) for Acinetobacter baumannii. The treatment approach should be guided by the most recent and highest quality study, which in this case is the 2014 practice guidelines for the diagnosis and management of skin and soft tissue infections by the Infectious Diseases Society of America 1. Key considerations include:

• Susceptibility testing to guide antibiotic selection, particularly for Acinetobacter baumannii, which exhibits varied resistance patterns 1.
• Source control through drainage of abscesses or removal of infected devices is crucial when applicable.
• Monitoring for drug toxicities, such as nephrotoxicity with vancomycin and colistin, and neurotoxicity with colistin, is essential.
• The combination approach is necessary due to the different resistance mechanisms employed by MRSA and Acinetobacter baumannii, including altered penicillin-binding proteins in MRSA and efflux pumps and enzymatic degradation of antibiotics in Acinetobacter baumannii. Some key points to consider in the treatment of MRSA include:
• Vancomycin is the parenteral drug of choice for treatment of infections caused by MRSA, with a recommended dosage of 30 mg/kg/d in 2 divided doses IV for adults and 40 mg/kg/d in 4 divided doses IV for children 1.
• Linezolid is an alternative option, with a recommended dosage of 600 mg every 12 h IV or 600 mg bid po for adults and 10 mg/kg every 12 h IV or po for children <12 y 1.
• Clindamycin is another option, with a recommended dosage of 600 mg every 8 h IV or 300–450 mg qid po for adults and 25–40 mg/kg/d in 3 divided doses IV or 30–40 mg/kg/d in 3 divided doses po for children 1. For Acinetobacter baumannii, the recommended treatment includes a carbapenem such as meropenem, with a dosage of 1 g every 8 hours, combined with colistin, with a loading dose of 9 million units, then 4.5 million units every 12 hours 1. It is essential to note that the treatment duration is typically 7-14 days, depending on the severity of the infection, site, and clinical response, and that these infections often occur in critically ill patients, requiring supportive care and monitoring for drug toxicities.

From the FDA Drug Label

The cure rates in microbiologically evaluable patients with MRSA skin and skin structure infection were 26/33 (79%) for linezolid-treated patients and 24/33 (73%) for vancomycin-treated patients Adjudication Committee success rates in the ITT population were 44.2% (53/120) in patients treated with daptomycin for injection and 41.7% (48/115) in patients treated with comparator The clinical success rates determined at 7 to 14 days after last dose of therapy (IV and oral) (TOC visit) were 88% (45/51) for daptomycin for injection and 77% (17/22) for comparator

The best treatment regimen for a patient with Methicillin-resistant Staphylococcus aureus (MRSA) and Acinetobacter baumannii infections is not explicitly stated in the provided drug labels. However, based on the available information:

• Linezolid has shown a cure rate of 79% in patients with MRSA skin and skin structure infections 2.
• Daptomycin has shown a success rate of 44.2% in patients with S. aureus bacteremia/endocarditis, including those with MRSA 3.
• Vancomycin has shown a cure rate of 73% in patients with MRSA skin and skin structure infections 2. It is essential to note that the treatment of Acinetobacter baumannii infections is not directly addressed in the provided drug labels. Therefore, the choice of treatment should be based on the specific clinical scenario, taking into account the severity of the infection, the patient's medical history, and the susceptibility of the pathogens to different antibiotics. It is crucial to consult with a healthcare professional to determine the most appropriate treatment regimen for the patient.

From the Research

Treatment Regimens for MRSA and Acinetobacter baumannii Infections

• The treatment of Methicillin-resistant Staphylococcus aureus (MRSA) and Acinetobacter baumannii infections requires careful consideration of the antimicrobial susceptibility patterns of the isolates 4, 5, 6, 7, 8.
• For MRSA infections, vancomycin, daptomycin, and linezolid are commonly used treatment options 5, 7, 8.
• The combination of vancomycin and ceftaroline has been shown to be effective in treating persistent MRSA bacteremia 7.
• For Acinetobacter baumannii infections, carbapenems, polymyxins, and tigecycline are potential treatment options 4, 6.
• The choice of treatment regimen should be guided by the susceptibility patterns of the isolate and the clinical context of the patient 4, 6.

Antimicrobial Susceptibility Patterns

• MRSA isolates are often resistant to multiple antimicrobial agents, including penicillin and ampicillin 5.
• Acinetobacter baumannii isolates can be resistant to multiple antimicrobial agents, including carbapenems and polymyxins 4, 6.
• The susceptibility patterns of MRSA and Acinetobacter baumannii isolates can vary depending on the geographic location and the specific strain of the organism 4, 6.

Clinical Outcomes

• The clinical outcomes of patients with MRSA and Acinetobacter baumannii infections can be improved with appropriate treatment regimens 5, 7, 8.
• The combination of vancomycin and ceftaroline has been shown to be effective in reducing the duration of MRSA bacteremia and improving clinical outcomes 7.
• The choice of treatment regimen should be guided by the clinical context of the patient and the susceptibility patterns of the isolate 4, 6.