A Precise Scale-Up Method to Predict Particle Delivered Dose in a Human Respiratory System Using Rat Deposition Data: An In Silico Study

As surrogates to human beings, rats are used occasionally to study the therapeutic impact of inhaled pulmonary drug particles in microscale. To speculate human responses from rat studies, scale-up factors are widely used to extrapolate particle lung deposition from rat to human. However, available scale-up methods are highly simplified and not accurate, because they directly use the human-to-rat ratios of body weights (RBW) or lung surface areas (RSA) as the scale-up factor. To find a precise scale-up strategy, an experimentally validated Computational Fluid-Particle Dynamics (CFPD) was employed to simulate the transport and deposition of microparticles in both human and rate respiratory systems, which encompasses the pulmonary routes from mouth/nose to airways up to Generation 17 (G17) for human and G23 for the rat. Microparticles with the same range of Stk/Fr were injected into both models with the airflow at resting conditions. Numerical results indicate that particles (with the size ranging from 1 to 13 μm for humans and 0.6 to 6 μm for rat) have similar deposition pattern (DP) and deposition fraction (DF) in both models, which are resulted from both inertial impaction and gravitational sedimentation effects. A novel correlation is proposed to predict DFs in both human and rat respiratory systems as a function of the ratio of Stokes number to Froude number (Stk/Fr). Using the correlation as the novel scale-up tool, inter-species extrapolations can be precisely done on predicting particle depositions in human respiratory systems based on the deposition data in rats obtained from animal studies.