Bacterial killing and the development of reduced vancomycin susceptibility during continuous-infusion vancomycin (CIV) therapy were dependent on the area under the concentration-time curve over 24 h divided by the MIC (ƒAUC 24 /MIC), with values of >240 (equivalent total serum AUC 24 /MICs of >480) being bactericidal and suppressing emerging resistance in methicillin-resistant Staphylococcus aureus (MRSA). Also, vancomycin therapy was less likely to be bactericidal and 4.4 times more likely to lead to reduced vancomycin susceptibility in health care-associated MRSA than in community-associated MRSA.