Figure 1: Crossing the blood brain barrier
There are several mechanisms by which drugs can cross the blood-brain barrier (BBB):
1. Passive movement of water-soluble agents across the BBB is negligible because of the tight junctions between endothelial cells.
2. Small, lipid-soluble agents, such as antidepressants, cross the BBB via diffusion through endothelial cells.
3. Specialised transport proteins transport glucose, amino acids, and drugs like vinca alkaloids and cyclosporine, across the BBB.
4. Receptors mediate transcytosis of proteins like insulin and transferrin.
5. Proteins, such as albumin, are adsorbed and transported across the BBB by transcytosis.
6. Efflux transporters counter passive diffusion by pumping foreign agents, such as non-sedating antihistamines, out of the brain.
Pharmaceutics 2014;6:557-583; Nature Reviews Neuroscience 2006;7:41-53