Dietary Route of Exposure for Rabbit Developmental Toxicity Studies

Dietary administration is a relevant route of oral exposure for regulatory toxicity studies of agrochemicals as it mimics potential human intake of the chemical via treated crops and commodities. Moreover, dietary administration of test compounds during a developmental toxicity study can deliver a prolonged and stable systemic exposure to the embryo or fetus at all stages of development. In this study, strategies were employed to optimize rabbit test material consumption via diet. Comparative toxicokinetic profiles of gavage versus dietary administration were evaluated in pregnant or non-pregnant New Zealand White rabbits for 2 novel agrochemicals with different plasma half-lives of elimination (sulfoxaflor, t_½ = 13.5 h and halauxifen, t_½ = 1 h). Dietary administration of sulfoxaflor resulted in stable 24-h plasma concentrations, whereas gavage administration resulted in a 3-fold fluctuation in plasma levels between C_max and C_min Dietary administration of sulfoxaflor resulted in a 2-fold higher nominal and diurnal systemic dose when compared with gavage dosing due to C_max-related maternal toxicity following gavage. Results with the shorter half-life molecule, halauxifen, were more striking with a 6-fold diurnal fluctuation by the dietary route compared with a 368-fold fluctuation between C_max and C_min by gavage. Furthermore, plasma halauxifen was detectable only up to 12 h following gavage but up to 24 h following dietary administration. Finally, the presence of these compounds in fetal blood samples was demonstrated, confirming that dietary exposure is appropriate for achieving fetal exposure. Collectively, the results of these studies support the use of dietary exposure in rabbit developmental toxicity studies.