Accordingly, the resistance rates of viridans group streptococci are similarly high in otherwise healthy individuals and in patients with serious underlying diseases. The impact of viridans group streptococcal resistance on antibiotic prevention of IE is unknown. If resistance in vitro is predictive of lack of clinical efficacy, the high resistance rates of viridans group streptococci provide additional support for the assertion that prophylactic therapy for a dental procedure is of little, if any, value. It is impractical to recommend prophylaxis with only those antibiotics, such as vancomycin or a fluoroquin- olone, that are highly active in vitro against viridans group streptococci. There is no evidence that such therapy is effective for prophylaxis of IE, and their use might result in the develop- ment of resistance of viridans group streptococci and other microorganisms to these and other antibiotics. In Table 5, amoxicillin is the preferred choice for oral therapy because it is well absorbed in the GI tract and provides high and sustained serum concentrations. For indi- viduals who are allergic to penicillins or amoxicillin, the use of cephalexin or another first-generation oral cephalosporin, clindamycin, azithromycin, or clarithromycin is recom- mended. Even though cephalexin was less active against viridans group streptococci than other first-generation oral cephalosporins in 1 study,136 cephalexin is included in Table 5. No data show superiority of 1 oral cephalosporin over another for prevention of IE, and generic cephalexin is widely available and relatively inexpensive. Because of possible cross-reactions, a cephalosporin should not be administered to patients with a history of anaphylaxis, angioedema, or urticaria after treatment with any form of penicillin, including ampicillin or amoxicillin. Patients who are unable to tolerate an oral antibiotic may be treated with ampicillin, ceftriaxone, or cefazolin administered intramuscularly or intravenously. 