From the Guidelines
Nafcillin is the most appropriate antibiotic for this patient. This patient presents with fever, anorexia, dyspnea, severe back pain, tachycardia, hypertension, and a history of intravenous (IV) drug use, with a diagnosis of Staphylococcus aureus bacteremia, presenting with a systolic murmur, which strongly suggests infective endocarditis caused by Staphylococcus aureus, confirmed by positive blood cultures. Nafcillin, an anti-staphylococcal penicillin, is the preferred treatment for methicillin-sensitive S. aureus (MSSA) infections, as recommended by the American Heart Association 1. The standard regimen would be nafcillin 2g IV every 4 hours for 4-6 weeks. While awaiting methicillin-sensitivity results, empiric coverage with nafcillin or oxacillin plus vancomycin may be considered given the possibility of methicillin-resistant S. aureus (MRSA) in this population, as suggested by the European Society of Cardiology 1.
Some key points to consider in the management of this patient include:
- The use of gentamicin as an adjunctive therapy is not recommended due to the lack of clinical benefit and increased risk of renal toxicity, as noted in the guidelines from the American Heart Association 1 and the European Society of Cardiology 1.
- Vancomycin is an alternative for patients who are allergic to penicillin or have methicillin-resistant S. aureus, with a recommended dosage of 30-60 mg/kg/day IV in 2-3 doses, as suggested by the European Society of Cardiology 1.
- The patient should be cared for in a medical facility with cardiothoracic surgery capabilities and infectious diseases consultation, as recommended by the American Heart Association 1.
- Decisions about outpatient therapy may be individualized based on clinical impression of symptomatic recovery, cardiovascular stability, and availability of infrastructure for outpatient monitoring, as suggested by the American Heart Association 1.
Overall, the management of this patient should prioritize the use of nafcillin as the primary antibiotic, with consideration of vancomycin as an alternative in certain situations, and careful monitoring for potential complications and adjustment of therapy as needed.
From the FDA Drug Label
Gentamicin Injection, USP is indicated in the treatment of serious infections caused by susceptible strains of the following microorganisms: ... Staphylococcusspecies (coagulase-positive and coagulase-negative) Gentamicin injection has also been shown to be effective in the treatment of serious staphylococcal infections.
The next most appropriate antibiotic for a patient with Staphylococcus aureus bacteremia is gentamicin (IV), as it is effective in treating serious staphylococcal infections, including those caused by Staphylococcus aureus 2, 2.
From the Research
Patient Profile
- Fever, anorexia, dyspnea, severe back pain, tachycardia, hypertension
- History of intravenous (IV) drug use
- Diagnosis of Staphylococcus aureus bacteremia
- Presenting with a systolic murmur
Treatment Approach
- The choice of antibiotic regimen depends on the species of Staphylococcus, its resistance pattern, the type of infected valve, the site of infection, and underlying conditions of the host 3
- For native valve endocarditis caused by methicillin-susceptible Staphylococcus aureus, penicillinase-resistant penicillins (e.g. oxacillin) are recommended 3, 4, 5
- The addition of an aminoglycoside (e.g. gentamicin) may be considered for certain cases 3, 6
- For methicillin-resistant Staphylococcus aureus, vancomycin is commonly used 3, 6, 4, 5
Recommended Antibiotic Regimens
- Oxacillin or nafcillin with or without gentamicin for native valve endocarditis caused by methicillin-susceptible Staphylococcus aureus 6
- Vancomycin for methicillin-resistant Staphylococcus aureus, with or without the addition of rifampicin or other agents 3, 6, 4, 5
- Cloxacillin alone or combined with gentamicin may be effective for short-term therapy of right-sided Staphylococcus aureus endocarditis 7