Impact of transport and drug properties on the local pharmacology of drug-eluting stents.

Drugs released from stents are driven by physiological transport forces, principally solvent-driven flow (convection) and random molecular agitation (diffusion). The relative strength of these two forces determines drug penetration and distribution in the arterial wall. Drug physicochemical factors can induce critical modulations to the primary distribution, both transiently and at steady state. Hydrophobic interactions and nonspecific binding, for example, can both result in tissue drug concentrations severalfold above administered concentration. Drug interaction with native proteins may also interfere with drug transfer at the stent-artery interface. These transport forces and tissue interactions can induce local drug concentrations even at steady state to vary by one or more orders of magnitude over the span of a few cells. To account for significant local variations in drug concentrations following stent-based delivery, rational design of vascular delivery systems requires consideration of drug distribution and tissue interactions on a local, continuum basis. Continuum analysis adapts traditional pharmacokinetics to the local environment by supplementing discrete global parameters of drug content with continuous local values of concentration, transport and binding. The interplay of these parameters with local flux conditions and drug and tissue properties defines the local drug distribution in space and over time. This type of analysis may well become increasingly relevant given the trend toward stent-based drug therapy in cardiovascular care.