Intravenous antibiotics are commenced soon after suffi¬cient blood cultures are obtained; usually a combination of nafcillin (oxacillin or flucloxacillin), ampicillin, and gentamicin is administered. Changes are made when the organism and antibiotic sensitivities are established.
Organisms that commonly cause endocarditis and appro¬priate antibiotic combinations include the following:
1. S. viridans or S. bovis: If the MIC to penicillin is less than 0.1 mg/ml, give penicillin (IV 2–3 million U every 4 h for 4 weeks) or 2 weeks IV then amoxicillin (orally 500 mg every 6 h for 2 weeks) or ampicillin/sulbactam (2 g every 6 h for 2 weeks IV) and then amoxicillin (orally 500 mg every 6 h for 2 weeks) or penicillin and gentamicin IV for 2 weeks or ceftriaxone 2 g once daily IV for 2 weeks. Then IV or IM therapy once daily given as an outpatient or in the home is cost saving; but IM ceftriaxone is painful.
2. Partially sensitive S. viridans or S. bovis, MIC penicillin greater than 0.1 mg/ml: penicillin (3 million U every 4 h IV) plus gentamicin (1–1.5 mg/kg every 8 h IV for 2 to 4 weeks) or, from the third week, amoxicillin (500 mg orally every 6 h for 2 weeks).
3. S. fecalis, S. fecium, S. durans, or similar fecal strep¬tococci are difficult to eradicate: If the length of illness is less than 3 months, it is advisable to give ampicillin/ sulbactam (IV 2–3 g every 6 h for 4 weeks) plus

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