ABSTRACT
The prime elements to be considered in successful site-specific drug delivery, besides the importance of the disease and the drug, are access, retention, and timing. Albumin microspheres containing methotrexate coupled to a monoclonal antibody against acute lymphoblastic leukemia, showed selective affinity for the antigen-positive human leukemia cell line Daudi and curtailed the growth of these cells in vitro. In physical targeting an external influence such as temperature or a magnetic field is used to direct the microspheres to the desired site and to cause the release of the content. Total blood flow, perfusion rates, and vessel permeability may vary significantly in tumors of similar histological origin in different patients, in different regions of the same tumor, and even in different metastases in the same patient. During the last decade microspheres and microcapsules, together with other types of colloidal carriers such as liposomes and emulsions, have been extensively studied for their ability to target to specific sites in the body.
