No abstract

Daptomycin is a novel cyclic lipopeptide antibiotic that provides rapid bactericidal activity against gram-positive pathogens in vitro, including methicillin-susceptible Staphylococcus aureus, methicillin-resistant S. aureus, vancomycin-resistant S. aureus, penicillin-resistant Streptococcus pneumoniae, and ampicillin- and vancomycin-resistant enterococci. The United States Food and Drug Administration recently approved daptomycin for treatment of complicated skin and skin-structure infections. Its efficacy in the treatment of more-serious infections (e.g., staphylococcal bacteremia) is under investigation. As an intravenous agent that is administered once per day, it offers a convenient regimen for therapy that is continued after discharge, with a side effect profile that appears minimal and manageable. Spontaneous acquisition of resistance in vitro is rare, and hopefully this characteristic will extrapolate into the clinical setting. The rapid bactericidal activity, low potential for resistance, and promising safety profile associated with this agent will make it a useful addition to our growing armamentarium of antibiotics active against gram-positive pathogens.

The Health Belief Model (Rosenstock, 1966) was constructed to explain which beliefs should be targeted in communication campaigns to cause positive health behaviors. The model specifies that if individuals perceives a negative health outcome to be severe, perceives themselves to be susceptible to it, perceives the benefits to behaviors which reduce the likelihood of that outcome to be high, and perceives the barriers to adopting those behaviors to be low, then the behavior is likely. A meta-analysis of 18 studies (2,702 subjects) was conducted to determine if measures of these beliefs could longitudinally predict behavior. Benefits and barriers were consistently the strongest predictors. The length of time between measurement of the HBM beliefs and behavior, prevention versus treatment behaviors, and drug taking regimens v. other behaviors were identified as moderators of the HBM variables’ predictive power.

Recently, the emergence of reduced susceptibility to daptomycin has been linked to the reduced vancomycin susceptibility that occurs after vancomycin exposure in Staphylococcus aureus in vivo and in vitro. This study evaluated this propensity in clinical isolates of S. aureus using an in vitro pharmacokinetic/pharmacodynamic model with simulated endocardial vegetations over 8 days. Five clinical isolates (four methicillin-resistant S. aureus isolates and one methicillin-susceptible S. aureus [MSSA] isolate), all of which were reported to have become nonsusceptible to daptomycin, were evaluated. The following regimens were evaluated: vancomycin 1 g every 12 h for 4 days followed by daptomycin 6 mg/kg of body weight daily for 4 days and daptomycin 6 mg/kg daily for 8 days. If nonsusceptibility was detected, the following regimens were evaluated: no treatment for 4 days followed by daptomycin 6 mg/kg daily for 4 days, vancomycin 1 g every 12 h for 4 days followed by daptomycin 10 mg/kg daily for 4 days, and daptomycin 10 mg/kg daily for 8 days. The emergence of daptomycin nonsusceptibility (12-to 16-fold MIC increase) was detected only with the MSSA isolate with daptomycin 6 mg/kg daily for 4 days after vancomycin exposure. However, the bactericidal activity of daptomycin was maintained and the MIC increases of these isolates, which had no mprF or yycG mutations, were unstable to serial passage on antibiotic-free agar. Subsequent regimens did not demonstrate nonsusceptibility to daptomycin. These findings suggest that reduced daptomycin susceptibility can be a strain-specific and unstable event. Further evaluation of the susceptibility relationship between daptomycin and vancomycin is necessary to understand the factors involved and their clinical significance.