Treatment
High dose antibiotics are administered by the intravenous route to maximize diffusion of antibiotic molecules into vegetation(s) from the blood filling the chambers of the heart. This is necessary because neither the heart valves nor the vegetations adherent to them are supplied by blood vessels. Antibiotics are continued for a long time, typically two to six weeks depending on the characteristics of the infection and the causative micro-organisms.
In acute endocarditis, due to the fulminant inflammation empirical antibiotic therapy is started immediately after the blood has been drawn for culture. This usually includes vancomycin and ceftriaxone IV infusions until the microbial identification and susceptibility report with the minimum inhibitory concentration becomes available allowing for modification of the antimicrobial therapy to target the specific microorganism. It should be noted that the routine use of gentamicin to treat endocarditis has fallen out of favor due to the lack of evidence to support its use (except in infections caused by Enterococcus and nutritionally variant streptococci) and the high rate of complications.
In subacute endocarditis, where patient's hemodynamic status is usually stable, antibiotic treatment can be delayed till the causative microorganism can be identified.
The most common organism responsible for infective endocarditis is Staphylococcus aureus, which is resistant to penicillin in most cases. High rates of resistant to oxacillin are also seen, in which cases treatment with vancomycin is required.
Viridans group streptococci and Streptococcus bovis are usually highly susceptible to penicillin and can be treated with penicillin or ceftriaxone.
Relatively resistant strains of viridans group streptococci and Streptococcus bovis are treated with penicillin or ceftriaxone along with a shorter 2 week course of an aminoglycoside during the initial phase of treatment.
Highly penicillin resistant strains of viridans group streptococci, nutritionally variant streptococci like Granulicatella sp., Gemella sp. and Abiotrophia defectiva, and Enterococci are usually treated with a combination therapy consisting of penicillin and an aminoglycoside for the entire duration of 4-6 weeks.
Selected patients may be treated with a relatively shorter course of treatment (2 weeks) with benzyl penicillin IV if infection is caused by viridans goup streptococci or Streptococcus bovis as long as the following conditions are met:
‣ Endocarditis of a native valve, not of a prosthetic valve
‣ An MIC ≤ 0.12 mg/l
‣ No intracardiac complication such as heart failure, abscess, or conduction defects
‣ No evidence of extracardiac complication like septic thromboembolism
‣ No vegetations > 5mm in diameter
‣ Rapid clinical response and clearance of blood stream infection
Additionally oxacillin susceptible Staphylococcus aureus native valve endocarditis of the right side can also be treated with a short 2 week course of beta lactam antibiotic like nafcillin with or without aminoglycosides
Surgical debridement of infected material and replacement of the valve with a mechanical or bioprosthetic artificial heart valve is necessary in certain situations:
‣ Patients with significant valve stenosis or regurgitation causing heart failure
‣ Evidence of hemodynamic compromise in the form of elevated end diastolic left ventricular or left atrial pressure or moderate to severe pulmonary hypertension
‣ Presence of intracardiac complications like paravalvular abscess, conduction defects or destructive penetrating lesions
‣ Recurrent septic emboli despite appropriate antibiotic treatment
‣ Large vegetations (> 10 mm)
‣ Persistent positive blood cultures despite appropriate antibiotic treatment
‣ Prosthetic valve dehiscence
‣ Relapsing infection in the presence of a prosthetic valve
‣ Abscess formation
‣ Early closure of mitral valve
‣ Infection caused by Fungi or resistant Gram negative bacteria
Infective endocarditis is associated with 18% in-hospital mortality.
Read more about this topic: Infective Endocarditis
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