A Shiny app modelling how an inhaled drug moves through the lung and body over time.
The model is hosted on Shinyapps.io as an interactive app. You can load a drug's parameters and watch the simulated concentration curves in each chosen region. This website was originally meant as supplementary data so please excuse the lack of annotation.
Attached below is a full parameter set for inhaled salbutamol. I found the numbers online personally using public data. Click below to download; it can be loaded directly into the Shiny app above. Check the boxes that you want to observe and please allow it at most 10 seconds to work, it is common for it to display an error as a placeholder message until the graph loads.
Pharmacokinetics is the study of what the body does to a drug: how it is absorbed, distributed around the body, metabolised, and eventually expelled. We treat as a concentration that changes over time in each location e.g., how much drug is sitting in the blood, the liver, the fat, every minute after drug admission. For inhaled drugs specifically, we account for the fact that the drug first has to land somewhere in the airways and cross through lung tissue, this will be observed as a steep initial gradient in the graph.
This app is built on a model that brings together four separate pieces of lung and body physiology into one system of roughly 70 simultaneous differential equations:
Full details can be found on the NIH.gov website. This allows us to create a complete model for inhaled drugs: how fast does it dissolve, how much is cleared away versus absorbed locally, and what does the resulting concentration curve look like everywhere else in the body. Historically, the hardest part of this question was the between-comparment interactions i.e., the drug can flow freely between neighbouring regions.