IE caused by staphylococci that are penicillin sus- ceptible should be treated with antistaphylococcal -lactam antibiotics rather than aqueous crystalline penicillin G because clinical laboratories are not able to detect penicillin susceptibility (Class I; Level of Evidence B). 5. Six weeks of nafcillin (or equivalent antistaphylo- coccal penicillin) is recommended for uncompli- cated left-sided NVE caused by MSSA; at least 6 weeks of nafcillin (or equivalent antistaphylococcal penicillin) is recommended for complicated left- sided NVE caused by this organism (Class I; Level of Evidence C). 6. Daptomycin may be a reasonable alternative to vancomycin for treatment of left-sided IE resulting from MRSA (Class IIb; Level of Evidence B). 7. Selection of daptomycin dosing should be assisted by infectious diseases consultation (Class I; Level of Evidence C). Therapy of MSSA IE in Patients Allergic to or Intolerant of -Lactams Therapy for MSSA IE in patients truly unable to tolerate -lactams is problematic. One decision analysis study con- cluded that patients with a questionable history of immediate- type hypersensitivity to penicillins in the context of IE caused by MSSA should be skin tested before starting antibiotic However, the limited availability of standardized skin test reagents makes testing impractical. Instead, most experts endorse one of the published standard desensitization protocols. For patients with a well-defined history of nonana- phylactoid reactions to penicillins (eg, simple skin rash), a first-generation cephalosporin such as cefazolin is reasonable. Although cefazolin may be more susceptible to -lactamase mediated hydrolysis than nafcillin157 and less effective in the treatment of MSSA experimental IE, the clinical significance of these observations is unknown. Many experts regularly use cefazolin for S aureus IE instead of nafcillin because of drug Table 10. 