Therapeutics Delivery Behind, Through and

The brain has five protective barriers (BPB) that hinder the delivery of therapeutic drugs. They describe the five main interfaces between the central nervous system (CNS) and the periphery. These include: the blood brain barrier (BBB) that extends down the spinal cord; the brain cerebrospinal fluid (CSF) barrier (B[CSF]B]; the brain-inner CSF barrier (B[iCSF] b); the brain-outer CSF barrier B[oCSF]B; and the brain retinal barrier (B[R]B). We shall mostly be concerned with the BBB and use the denomination BBB as if it applied (though erroneously) to all BPBs.