Abstract-Successful implementation of local arterial drug delivery requires transmural distribution of drug. The physicochemical properties of the applied compound, which govern its transport and tissue binding, become as important as the mode of delivery. Hydrophilic compounds distribute freely but are cleared rapidly. Hydrophobic drugs, insoluble in aqueous solutions, bind to fixed tissue elements, potentially prolonging tissue residence and biological effect. Paclitaxel is such a hydrophobic compound, with tremendous therapeutic potential against proliferative vascular disease. We hypothesized that the recent favorable preclinical data with this compound may derive in part from preferential tissue binding as a result of unique physicochemical properties. The arterial transport of paclitaxel was quantified through application ex vivo and measurement of the subsequent transmural distribution. Arterial paclitaxel deposition at equilibrium varied across the arterial wall and was everywhere greater in concentration than in the applied drug source. Permeation into the wall increased with time, from 15 minutes to 4 hours, and varied with the origin of delivery. In contrast to hydrophilic compounds, the concentration in tissue exceeds the applied concentration and the rate of transport was markedly slower. Furthermore, endovascular and perivascular paclitaxel application led to markedly differential deposition across the blood vessel wall. These data suggest that paclitaxel interacts with arterial tissue elements as it moves under the forces of diffusion and convection and can establish substantial partitioning and spatial gradients across the tissue.

Local vascular drug delivery systems provide elevated concentrations in target arterial tissues, while minimizing systemic side effects. Drug can now be released to isolated arterial segments from the endovascular or perivascular aspects of the blood vessel, yet the forces that determine drug distribution and deposition for these different modes of delivery have not been rigorously investigated. This study examines mechanisms of transmural transport of a model vasoactive drug, heparin, and compares estimates of the distribution after administration from either aspect of the artery. We showed that (1) heparin traversed the arterial wall rapidly; (2) diffusion far outweighed convection in the control of transmural heparin transport in the normal artery, but after endothelial injury, convective forces rose to one quarter the magnitude of diffusive forces; (3) the endothelium posed a minimal diffusive barrier to heparin; and (4) the diffusive barrier imposed by the adventitia depended on its thickness. These findings strongly suggest that vasoregulatory compounds can be administered to target tissue by either perivascular or endovascular means with equal efficacy, because the forces governing transport of heparin from either aspect of the blood vessel wall are not significantly different. Furthermore, the differences in arterial transport properties between heparin and other macromolecules suggest that distribution and the optimal aspect of delivery will depend just as much on the physicochemical properties of the drug as the state of the blood vessel wall.