What is the recommended short-term antibiotic treatment for a patient with endocarditis caused by Methicillin-Sensitive Staphylococcus aureus (MSSA) who is an intravenous (IV) drug user?

From the Guidelines

For intravenous drug users with methicillin-sensitive Staphylococcus aureus (MSSA) endocarditis, the standard treatment is a 4-6 week course of intravenous antibiotics, typically nafcillin or oxacillin at 2 grams IV every 4 hours. This recommendation is based on the most recent and highest quality study available, which emphasizes the importance of prolonged antibiotic treatment to fully eradicate the infection 1. The use of gentamicin in addition to nafcillin or oxacillin is not recommended due to the lack of clinical benefit and increased risk of renal toxicity 1.

Key considerations in the treatment of MSSA endocarditis include:

• The use of semisynthetic, β-lactamase–resistant penicillins (nafcillin or oxacillin) for a minimum of 4 to 6 weeks 1
• The importance of monitoring for signs of treatment failure, including blood cultures, echocardiography, and clinical assessment 1
• The need for ongoing substance use disorder treatment during antibiotic therapy 1
• The potential use of alternative antibiotics, such as cefazolin or vancomycin, in patients with penicillin allergy or intolerance 1

It is essential to note that short-term antibiotic therapy (less than 4 weeks) is generally not recommended for MSSA endocarditis due to high rates of relapse and treatment failure. However, in carefully selected cases with uncomplicated right-sided endocarditis and rapid clinical response, some experts may consider a shortened course of treatment 1. Ultimately, the treatment of MSSA endocarditis should be individualized based on the patient's specific clinical circumstances and guided by the most recent and highest quality evidence available.

From the FDA Drug Label

DOSAGE AND ADMINISTRATION Bacteriologic studies to determine the causative organisms and their susceptibility to oxacillin should always be performed. Duration of therapy varies with the type of severity of infection as well as the overall condition of the patient, therefore it should be determined by the clinical and bacteriological response of the patient In severe staphylococcal infections, therapy with oxacillin should be continued for at least 14 days. RECOMMENDED DOSAGES FOR OXACILLIN FOR INJECTION, USP Drug Adults Oxacillin 250 to 500 mg IM or IV every 4 to 6 hours (mild to moderate infections) 1 gram IM or IV every 4 to 6 hours (severe infections)

The recommended short-term antibiotic treatment for a patient with endocarditis caused by Methicillin-Sensitive Staphylococcus aureus (MSSA) who is an intravenous (IV) drug user is oxacillin 1 gram IV every 4 to 6 hours for at least 14 days. Therapy should be continued for at least 48 hours after the patient has become afebrile, asymptomatic, and cultures are negative 2.

From the Research

Recommended Short-Term Antibiotic Treatment

For a patient with endocarditis caused by Methicillin-Sensitive Staphylococcus aureus (MSSA) who is an intravenous (IV) drug user, the recommended short-term antibiotic treatment is:

• A penicillinase-resistant penicillin, such as cloxacillin or oxacillin, for 2 weeks 3, 4
• The use of gentamicin in addition to cloxacillin or oxacillin does not appear to provide any therapeutic advantages for right-sided endocarditis 3
• Continuous infusion of oxacillin may be an effective alternative to intermittent infusion for the treatment of infective endocarditis caused by MSSA 5

Key Considerations

• The treatment regimen should be based on the species of Staphylococcus, its resistance pattern, the type of infected valve, and the presence of underlying conditions such as IV drug abuse 4
• Shorter treatment durations (2 weeks) may be considered for uncomplicated cases of right-sided endocarditis 4
• The American Heart Association guidelines for the diagnosis and treatment of infective endocarditis do not address continuous-infusion oxacillin, but it may be considered as an effective alternative to intermittent infusion 5

Additional Options

• Other antibiotic regimens, such as penicillin G or cephalosporins, may be considered for the treatment of infective endocarditis caused by MSSA, but the recommended duration of treatment is typically 4-6 weeks 6