Identification of optimal spray formulation and device features for enhancing intra-airway drug delivery to the nasopharynx

The nasopharynx, comprising the upper part of the pharynx located at the back of the nose, serves as a critical hotspot for respiratory infection onset, largely owing to the presence of specific surface receptors that pathogens can exploit for cell invasion, combined with a relatively sparse local mucociliary substrate. To enhance therapeutic efficacy of treatments during the initial stages of disease, it is thus essential to improve the delivery of drugs to the nasopharynx. This study uses high-fidelity LES models of breathing and sprayed particle transport to figure out the dependence of spray and formulation features on nasopharyngeal deposition. The simulations in two representative CT-based respiratory tract geometries have considered a feasible range of sprayed particle sizes (10 – 50 microns), six different formulation densities (1 – 1.5 g/mL), and twelve different plume angles (15 to 70 degrees). Results indicate that optimal deposition at the nasopharynx occurs with particle sizes between 25 – 40 microns, regardless of formulation density. Additionally, a formulation density of 1.2 g/mL and plume angles less than 60 deg. yielded the highest deposition rates. The experimentally validated findings can guide improved device and formulation designs for airway pharmaceutics.