Novel drug delivery systems: opportunities and caveats.

Programmed infusion pumps, polymers and neural transplants provide the capability of delivering a variety of agents to specific locations in the central nervous system. If a necessary or therapeutically useful substance cannot otherwise penetrate the blood-brain barrier, or must be delivered to a precise location in the CNS, these strategies may be of value in neurologic disease. The possibility of transplanting functioning tissue into the brain raises the hope of providing "new parts for old." For drugs that can penetrate the blood-brain barrier, and do not require a single precise anatomic site of action, systemic administration remains the "gold standard." The role of these novel drug delivery systems in treatment of Alzheimer's disease is as yet unclear.