In other studies, resistance of viridans group streptococci to penicillin ranged from 17% to 50%137 142 and resistance to ceftriaxone ranged from 22% to 42%.131,140 Ceftriaxone was 2 to 4 times more active in vitro than cefazolin.131,140 Similarly high rates of resistance were reported for macrolides, ranging from 22% to 58%137,141,143,144; resistance to clindamycin ranged from Most of the strains of viridans group streptococci in the above-cited studies were recovered from patients with serious underlying illnesses, including malignancies and febrile neu- tropenia. These patients are at increased risk of infection and colonization by multiple-drug resistant microorganisms, in- cluding viridans group streptococci. Accordingly, these Table 4. Dental Procedures for Which Endocarditis Prophylaxis Is Reasonable for Patients in Table 3 All dental procedures that involve manipulation of gingival tissue or the periapical region of teeth or perforation of the oral mucosa* *The following procedures and events do not need prophylaxis: routine anesthetic injections through noninfected tissue, taking dental radiographs, placement of removable prosthodontic or orthodontic appliances, adjustment of orthodontic appliances, placement of orthodontic brackets, shedding of deciduous teeth, and bleeding from trauma to the lips or oral mucosa. strains may not be representative of susceptibility patterns of viridans group streptococci recovered from presumably nor- mal individuals who undergo a dental procedure. Diekema et al137 reported that 32% of strains of viridans group strepto- cocci were resistant to penicillin in patients without cancer. King et al144 reported erythromycin resistance in 41% of streptococci recovered from throat cultures in otherwise healthy individuals who presented with mild respiratory tract infections. In that study, after treatment with either azithro- mycin or clindamycin, the percentage of resistant streptococci increased to 82% and 71%, respectively. Accordingly, the resistance rates of viridans group streptococci are similarly high in otherwise healthy individuals and in patients with serious underlying diseases. 