The Blood-Cerebrospinal Fluid Barrier in Man

The concept of a barrier between blood and cerebrospinal fluid (CSF) has its origins in the many observations concerning the relative exclusion of certain drugs from the fluids of the central nervous system. A standardized technique was developed for a study of the quantitative aspects of transfer of drugs or metabolites across the blood-cerebrospinal fluid barrier in the dog.¹ These drug distribution studies indicated that the plasma-CSF barrier is less of a special barrier than had been realized, and that, as far as the behavior of certain organic compounds, it would appear to have properties similar to other biological membranes. As with other membranes, the primarily lipoid nature of this barrier has been noted.^1-3 Drugs which enter CSF rapidly and extensively are in general lipoid soluble and undissociated at body pH. Those drugs excluded from CSF are lipoid insoluble and dissociated at body pH since ionized moieties do