DRUG TARGETING TO BRAIN : A REVIEW

The challenge in drug targeting is not only the targeting of drug to a specific site but also retaining itfor the desired duration to elicit pharmacological action. For a nanosystem administered intravenously,the first and foremost barrier is that of the vascular endothelium and the basement membrane. Also,plasma proteins have the ability to affect the biodistribution of drug carrier systems introduced in theblood stream. The in vivo biodistribution and opsonization of nanosystems in blood circulation isgoverned by their size and surface characteristics. For the nanosystem to remain in blood circulationfor a long time, the major problem is to avoid its opsonization and subsequent uptake by the phagocyticcells. The tight endothelial cells in brain constitute the blood brain barrier (BBB), which restricts theentry of most drugs and delivery systems. However vascular endothelium is not uniform throughout.Another barrier is that of the extracellular matrix, which should be crossed to access the target cellsin a tissue. If the whole tissue constitutes a target then the uniform distribution of drug throughout thetissue is another problem.