BACKGROUND:The European Centre for the Validation of Alternative Methods (ECVAM) designed the Embryonic Stem Cell Test (EST) as a tool for classifying developmentally toxic compounds. An in vitro tool to assess developmental toxicity would be of great value to the pharmaceutical industry to help with toxicity-associated attrition. METHODS: ECVAM's EST protocol was used, but employing a different mouse embryonic stem cell (ESC) line and an alternative differentiation medium. A subset of the compounds used to validate the EST assay along with a number of in-house pharmaceutical compounds plus marketed pharmaceutical compounds were used to assess the EST performance with receptor-mediated compounds. RESULTS: Our results with ECVAM compounds mirrored ECVAM's. Compounds that were developmentally toxic in vivo were classified by the EST as moderate risk. Overall, the accuracy was 75% with the current set of data and the predictivity of low-, moderate-, and high-risk compounds was 90, 71, and 60% while the precision was 59, 86, and 100%, respectively. Interestingly, a number of the non-developmentally toxic compounds had values for the 3T3 IC 50 values, which were lower than the ESC IC 50 and ID 50, a situation not taken into account by ECVAM when designing the EST algorithm. CONCLUSIONS: The assay as currently constructed has a significant falsepositive rate (B40%), but a very low false-negative rate (B7%). Additional moderate-and high-risk compounds need to be assessed to increase confidence, accuracy, and understanding in the EST's predictivity. Birth Defects Res (Part B) 83: 104-111, 2008.

The efficacy of linezolid, alone or in combination with rifampin, against methicillin-susceptible Staphylococcus aureus in rabbits with experimental endocarditis was investigated. Linezolid (50 or 75 mg/kg of body weight), rifampin, and linezolid (25, 50, or 75 mg/kg) plus rifampin produced statistically significant reductions in bacterial counts compared with those in untreated controls. Plasma or valvular vegetation levels of linezolid in the groups treated with the linezolid-rifampin combination were similar to those in the respective linezolid-only treatment groups. At therapeutic levels of linezolid, rifampin resistance was not observed. The results from this experimental model of endocarditis suggest that while rifampin did not provide synergy to the linezolid dosing, it did not antagonize the efficacy of linezolid.

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