The mainstay of treatment of bacterial endocarditis is intravenous antibiotics. Empiric therapy should be based on the characteristics of the given patient, whether an artificial valve is or is not involved, and local resistance patterns. Ultimately, definitive therapy should be based on the results of the blood culture and sensitivity.
Empiric antibiotic therapy for endocarditis is tailored to cover the organisms that are most likely to infect a given patient group. For uncomplicated IE, bacteria commonly found in the upper respiratory tract, gastrointestinal tract, and skin are likely to be the causative bacterium in patients with native-valve endocarditis acquired in the community. These include staphylococci, viridans streptococci, and Streptococcus bovis, as well as the "HACEK" organisms (Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, and Kingella); therefore, for empiric therapy for uncomplicated native-valve IE, intravenous ceftriaxone or nafcillin plus gentamicin is recommended. If the incidence of methicillin-resistant S aureus (MRSA) is high, vancomycin should be used.
Complicated IE includes hospital-acquired infections, intravenous drug use, and artificial valve infections. Patients with hospital-acquired infections or intravenous drug use are more likely to have infection due to S aureus. Other common organisms for this patient population include gram-negative bacteria, such as Pseudomonas aeruginosa, group D enterococci, and fungal species (such as Candida ). Patients with suspected MRSA infection, intravenous drug use, or suspected hospital-acquired infections should be empirically treated with a combination of vancomycin and gentamicin.
For patients with artificial valves, the organisms are most likely to be S aureus and other coagulase-negative Staphylococcal species, enterococci, and gram-negative bacilli; therefore, these patients should be empirically treated with gentamicin, vancomycin, and rifampin. Rarely, patients with blood culture-negative endocarditis may be colonized with fastidious organisms, such as Granulicatella species, Abiotrophia species, Bartonella,Coxiella burnetii, Brucella, and Tropheryma whipplei.
Prophylaxis for patients with high-risk cardiac conditions (such as prosthetic heart valve or previous IE) is indicated when they are undergoing certain procedures. Amoxicillin or ampicillin is indicated for nonpenicillin-allergic patients 1 hour before the procedure. For penicillin-allergic patients, premedication with clarithromycin, azithromycin, clindamycin, cephalexin, cefazolin, or ceftriaxone is appropriate. Antibiotic or practice guideline references should be consulted before recommending prophylaxis.
The patient in this case was admitted and underwent TEE that confirmed the presence of 2 distinct lesions on the aortic valve suspicious for vegetations. He was started on a course of intravenous antibiotics, but unfortunately, he once again left the hospital against medical advice before completion of therapy.
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