Paper Title
Predicting the Plasma Concentration of Flusilazole in Humans from in Vitro Toxicokinetic Data using PBTK Modelling: Implications in Health Risk Assessment

Abstract
Fungicides are chemicals that are widely used in agriculture to control or prevent the damage caused by fungal organisms and their spores. Flusilazole (FLZ) is a registered and extensively used azole fungicide in India. It is known to be a genotoxic, embryotoxic as well as a potent endocrine disruptor. Toxicokinetic data is crucial in deriving a relationship between external exposure and internal dose. It is useful in risk assessment studies for designing and interpretation of toxicity data and for reducing the uncertainty. However, the toxicokinetic data available for FLZ is very limited. The 21st century is moving towards non-animal approaches, where toxicokinetic (TK) models are assisting in the in vitro to in vivo extrapolation, thus reducing the number of animals required for the in vivo studies. In the present work, we aimed to predict the human in vivo toxicokinetic profile of FLZ using in vitro data with the help of Simcyp™ software. To the best of our knowledge, there is no existing TK model for flusilazole for its risk assessment. The physico-chemical properties of FLZ, such as molecular weight (315.39), dissociation constant ( pka = 2.5), partition co-efficient, (logP = 3.7), were obtained from literature. The fraction unbound to plasma (fu) was determined using plasma protein binding studies, and the value was found to be 0.038. The permeability in terms of Papp(A-B) was determined using Caco-2 permeability data and was found to be 33.6e-6 cm/sec. The intrinsic clearance (CLint) obtained from metabolic stability was 9.135 mL/min/mg. These properties of FLZ were used as inputs for the developing model in humans. The human toxicokinetic parameters were successfully predicted at ADI. The developed model can be used for risk assessment of flusilazole in humans and for the interpretation of biomonitoring data.