INITIAL INTERLABORATORY VALIDATION-STUDY OF FETAX - PHASE-I TESTING

An interlaboratory validation study was undertaken to evaluate the rep eatability and reliability of the Frog Embryo Teratogenesis Assay-Xeno pus (FETAX), which is a whole embryo developmental toxicity screening assay. A three-phase experimental program with seven participants was carried out. Phase I was a training and protocol evaluation phase wher e the identity of the three test materials was known. Hydroxyurea, iso niazid and 6-aminonicotinamide were tested in Phase I. Because the che micals has been tested previously in FETAX, the same concentrations ne eded to establish the 96-h median lethal concentration (LC(50)) and th e concentration inducing malformations in 50% of the surviving embryos (EC(50)) were used by all laboratories. The results of Phase I are pr esented in this report, and FETAX has proved to be as repeatable and r eliable as many other bioassays. Some excess variation was observed in individual laboratories. Some of this variation may have been due to training difficulties. One change in protocol design necessitated by t his study was the use of 6-aminonicotinamide as a reference toxicant. While 6-aminonicotinamide provided excellent concentration-response da ta in most laboratories, the protocol was written too strictly based o n historical FETAX data. Phases II and m are currently in progress.