Bacterial endocarditis (BE) is relatively rare; however, it is life-threatening with mortality rates of over 20%, and is more frequent in the elderly. Prophylaxis with antibacterial drugs is recommended before procedures commonly associated with BE based on the associated micro-organism and cardiac condition of the patient. According to the American Heart Association guidelines, oral amoxicillin is the standard antibacterial regimen for oral, dental, respiratory tract and oesophageal procedures (most often associated with the viridans streptococci group). Parental antibacterials are most often recommended for patients prior to gastrointestinal and genitourinary procedures (commonly associated with enterococci). The recommendation for high-risk patients is intramuscular or intravenous ampicillin plus gentamicin. In penicillin-allergic individuals, vancomycin plus gentamicin is advocated. Either oral amoxicillin or parenteral ampicillin is recommended for moderate-risk patients. Identification of the causative bacteria determines the treatment of BE. Streptococci and staphylococci cause approximately 80% of cases of BE with the remainder of cases associated with other Gram-positive organisms including enterococci and the HACEK group of organisms. Four weeks of benzylpenicillin (or ceftriaxone) is the preferred regimen for uncomplicated cases of endocarditis due to penicillin-susceptible viridans streptococci or Streptococcus bovis in most patients. The combination of benzylpenicillin and gentamicin is recommended when endocarditis is caused by enterococci or by relatively penicillin-resistant strains of viridans streptococci or S. bovis. The preferred regimen for staphyococcal endocarditis on native heart valves is nafcillin or oxacillin with or without gentamicin; on prosthetic valves the treatment of choice is nafcillin or oxacillin, in combination with both rifampicin and gentamicin. For patients allergic to penicillin, vancomycin with or without gentamicin is recommended as a replacement for the penicillin plus gentamicin component in all the above regimens. Outpatient therapy may be suitable in selected patients with BE.
