-Lactam efficacy, in contrast, is best predicted by the percent duration of time that the serum concentration exceeds the MIC.102 For peni- cillins and cephalosporins to achieve a bacteriostatic effect in a murine model, the time the free drug must exceed the MIC is 35% to 40% of the dosing interval, whereas a bac- tericidal response requires 60% to 70% of the dosing inter- Two retrospective studies examined the continuous infusion of 2 -lactams (cefazolin and oxacillin) for meth- icillin-sensitive S aureus (MSSA) infections, including IE, with results supporting continuous infusion of these drugs. More study is needed, however, before a strong recommen- dation can be made.105,106 For concentration-dependent antibiotics such as amino- glycosides and fluoroquinolones, a ratio of maximum serum concentration to MIC of >10 was associated with improved efficacy in patients with Gram-negative pneumonia, whereas /MIC >125 was associated with an improved clini- cal efficacy for ciprofloxacin against infections caused by Liu et al109 demonstrated that the minimal AUC24 /MIC requirement for daptomycin with an 80% kill efficacy in a S aureus infection mouse model was 250, which would be easily achieved by the recommended for complicated bacteremia, including right-sided IE. Some experts have recommended daptomycin doses of 8 for the treatment of complicated methicillin- resistant S aureus (MRSA) bacteremia, particularly IE. 