Adsorption of a Lipophilic Drug, Felodipine, at Different Interfaces

In connection with the development of methods for the delivery of lipophilic drugs in a bioavailable form, we have employed an integrated approach to the investigation of the adsorption of an antihypertensive drug, felodipine, at interfaces that simulate the surfaces of different carriers. Isotherms have been plotted for felodipine adsorption from solutions in heptane (C = 2.13 × 10–5 − 4.26 × 10–4 M) at interfaces with water and silver metal, as well as for the compression of drug monolayers formed on a water surface from the heptane solutions. The quantitative characteristics of the studied felodipine layers have been determined, and their phase state and the most probable conformation of adsorbed drug molecules have been analyzed taking into account the data of molecular dynamics simulations. The phase state of the felodipine layers at the heptane/water interface is adequately described by the van Laar equation. A bilayer is formed at the silver surface. A phase transition from a gaseous state to a liquid-expanded state has been revealed for the felodipine layers.