Regimens for Procedures on Infected Skin, Skin Structure, or Musculoskeletal Tissue These infections are often polymicrobial, but only staphylococci and -hemolytic streptococci are likely to cause IE. For patients with the conditions listed in Table 3 who undergo a surgical procedure that involves infected skin, skin structure, or musculo- skeletal tissue, it may be reasonable that the therapeutic regimen administered for treatment of the infection contain an agent active against staphylococci and -hemolytic streptococci, such as an antistaphylococcal penicillin or a cephalosporin (Table 5 for dosage; Class IIb, LOE C). Vancomycin or clindamycin may be administered to patients unable to tolerate a -lactam or who are known or suspected to have an infection caused by a methicillin- resistant strain of staphylococcus. A summary of the major changes in these updated recom- mendations for prevention of IE compared with previous AHA recommendations is shown in Table 6. Specific Situations and Circumstances Patients Already Receiving Antibiotics If a patient is already receiving long-term antibiotic therapy with an antibiotic that is also recommended for IE prophy- laxis for a dental procedure, it is prudent to select an antibiotic from a different class rather than to increase the dosage of the current antibiotic. For example, antibiotic regimens used to prevent the recurrence of acute rheumatic fever are administered in dosages lower than those recom- mended for the prevention of IE. Individuals who take an oral Table 6. Summary of Major Changes in Updated Document We concluded that bacteremia resulting from daily activities is much more likely to cause IE than bacteremia associated with a dental procedure. We concluded that only an extremely small number of cases of IE might be prevented by antibiotic prophylaxis even if prophylaxis is 100% effective. 