The National Toxicology Program is exploring the feasibility of adopting microencapsulation as an alternative means of incorporating volatile, reactive, and/or unpalatable chemicals into animal feed for toxicologic studies. Oral (dosed-feed) toxicology studies are performed on those chemicals which are demonstrated to be adequately stabilized in the microcapsules, but released into the gastrointestinal tract to allow biological availability. Trichlroethylene, 2-ethyhexanol, and methyl chloroform have been stabilized in microcapsules and evaluated for palatability and bioavailability in Fischer 344 rats. In each case, the absorption of the microencapsulated chemical was equivalent to that of the neat compound administered by gavage to Fischer 344 rats. In 14- day repeated-dose studies in F344 rats, similar toxic effects were produced by microencapsulated chemical given in feed as that of the neat chemical dissolved in corn oil administered by gavage. These studies indicate that microcapsulation can provide an excellent alternative method for studying the oral toxicological properties of volatile chemicals in laboratory animals. Future work will involve bioequivalence studies and toxicologic characterization of other microencapsulated chemicals.
