The following regimens are those commonly recommended:
1. Initial (best guess) treatment should comprise benzylpenicillin 1.2-2.4 g 4-hourly, plus gentamicin in low dose, e.g. 80 mg 12-hourly, by i.v. injection (synergy allows this dose of gentamicin and minimises risk of adverse effects). Regular serum gentamicin assay is vital: trough concentrations should be below 1 mg/1 and peak concentrations about 3 mg/1; if Staphylococcus aureus is suspected, high-dose flucloxacillin plus either gentamicin or sodium fusidate should be used. Patients allergic to penicillin should be treated with vancomycin.
2. When an organism has been identified and its sensitivity to drugs determined:
• Viridans group streptococci: benzylpenicillin plus gentamicin i.v. for at least 4 weeks or, if the organism is very sensitive, for 2 weeks, followed by amoxicillin p.o. for 2 weeks. Some patients with uncomplicated endocarditis caused by very sensitive strains may be managed as outpatients; for these patients ceftriaxone may be suitable, with its prolonged t1/, allowing convenient once-daily administration.
• Enterococcus faecalis (Group D): benzylpenicillin 1.8-3g 4-hourly plus gentamicin i.v. for 4-6 weeks. The prolonged gentamicin administration carries a significant risk of adverse drug reactions, but is essential to assure eradication of the infection.
• Staphylococcus aureus: flucloxacillin 2 g 4-hourly by i.v. injection for at least 4 weeks plus either gentamicin by i.v. injection or sodium fusidate by mouth for the first 1-2 weeks.
• Staphylococcus epidermidis and other coagulase negative staphylococci infecting native heart valves should be managed as for Staphylococcus aureus if the organism is sensitive. These organisms, however, have a predilection for prosthetic valves and such cases should be treated with vancomycin plus rifampicin for at least 6 weeks with gentamicin for the first 2 weeks.
• Coxiella or Chlamydia: tetracycline by mouth for at least 4-6 weeks. Valve replacement is advised in most cases, but some may continue indefinitely on tetracycline.
• Fungal endocarditis: amphotericin plus flucytosine are used. Valve replacement is usually essential.
• Culture-negative endocarditis: benzylpenicillin plus gentamicin i.v. are given for 4-6 weeks.
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