For many years, drug delivery systems were composed of simple pills, eyedrops, ointments, or intravenous solutions. Recently, materials have begun to play a major role in improving drug delivery. Drugs are now chemically attached to polymers, entrapped in small vesicles that are injected into the bloodstream, or put in pumps or polymeric materials that are placed in the body. These new materials-based systems are beginning to change the way drugs can be administered and, in so doing, have improved human health. This article provides a brief review of the major classes of drug delivery systems; a recent paper discusses these issues in detail.

Chemically attaching a drug to a polymer may alter such properties as its distribution in the body, rate of appearance in certain tissues, solubility, or antigenicity. For example, drugs have been linked to soluble macromolecules such as proteins, polysaccharides, or synthetic polymers via degradable linkages. This alters the drug's size and other properties, resulting in a different bodily drug distribution pattern. One example involves coupling the antitumor agent neocarzinostatin to styrene-maleic acid copolymers. When this complex was injected intra-arterially in patients with liver cancer, tumor size decreased significantly. In animals, the antitumor agent, doxorubicin, bound to N(2-hydroxypropyl) methacrylamide copolymers reduced toxicity. The plasma half-life and the drug levels in the tumor increased while the concentrations in the rest of the body decreased.