The study employs the Discrete Phase Model (DPM) and the Eulerian Wall Film (EWF) to provide a more accurate prediction of drug deposition in the respiratory airways. The methodology suggests that microscopic liquid medication particles are breathed, which, when they strike the lung airways, form a thin coating of the therapeutic component. The EWF model simulates the deposition and spread of the drug layer using the Eulerian approach to combat respiratory viruses. This allows for a more precise prediction of the post-impact dynamics of drug layer spread, an area where previous studies were limited. Parametric studies were conducted with three particle sizes 1 µm, 5 µm, and 10 µm at flow rates of 15, 30, and 60 liters per minute (LPM). Results show that in the fourth airway generation (G4), film thickness (FT) increased by 68.75% compared to G1 for 10 µm particles at a flow rate of 15 LPM. Furthermore, at the G4 level, 10 µm particles showed much better deposition efficiency than 1 µm particles (10.4 times) and 5 µm particles (6.54 times). Therefore, for effective patient treatment, particle sizes between 5 and 10 µm are recommended, as smaller particles (< 5 µm) may pose health risks by reaching deeper into the lungs, while larger particles (> 10 µm) tend to deposit in the oral cavity.