(PM3B) CNS Drug Delivery Flashcards
What are the compartments of the brain?
(1) Blood
(2) Cerebrospinal fluid
(3) Brain
Where is cerebrospinal fluid held?
(1) Ventricles
(2) Subarachnoid + intrathecal spaces
What is the volume of the cerebrospinal fluid?
140mL
What is the rate of production of cerebrospinal fluid?
35 mL/hr
At what rate does blood flow through the brain?
60 L/hr
What barrier is between the brain and the blood?
Blood brain barrier
What barrier is between the blood and the cerebrospinal fluid?
(1) Arachnoid villi
(2) Chloroid plexus
What barrier is between the cerebrospinal fluid and the brain?
Ependyma
What is the blood brain barrier?
Tight junctions between cells
Blocks diffusion of polar solutes
Limited paracellular pathways
How is the blood brain barrier selective?
Brain capillaries have restricted permeability compared to peripheral capillaries
Permeability restricted to <600Da (small molecules) + lipophilic substances
How do cells in the brain get solutes?
(1) Small lipophilic drugs diffuse freely
(2) Carrier-mediates transport of glucose/ amino acids/ proteins from high to low concentration
What are efflux pumps?
Transporters
Responsible for extruding drugs from brain
ATP-binding cassette transporter P-gp + multidrug resistant protein are key principles of efflux mechanism
What are some strategies for CNS drug delivery?
(1) Between tight junctions of BBB
(2) Through BBB –enhancement of transport across the endothelium
(3) Around the BBB – direct intracranial drug delivery
What is intracarotid drug delivery?
Injection directly into carotid artery
What is the role of osmotic agents in CNS drug delivery?
Strategy to cross BBB
Usually hypertonic mannitol
(1) 25% solution infused into carotid artery over 30 seconds
(2) Injection of drug through same cannula it can freely diffuse into the CNS