Week 9 - Chapter 20 Introduction to Central Nervous System Pharmacology

Question 1

Blood Brain Barrier

Answer 1

• –The blood-brain barrier impedes the entry of drugs into the brain. Passage across the barrier is limited to lipid-soluble agents and to drugs that cross by way of specific transport systems. Protein-bound drugs and highly ionized drugs cannot cross.
• –From a therapeutic perspective, the blood-brain barrier is a mixed blessing. The barrier protects the brain from injury by potentially toxic substances, but it can also be a significant obstacle to entry of therapeutic agents.
• –The blood-brain barrier is not fully developed at birth. Accordingly, infants are much more sensitive to CNS drugs than are older children and adults.

Question 2

Physical Dependence

Answer 2

• –sPhysical dependence is a state in which abrupt discontinuation of drug use will precipitate a withdrawal syndrome.
• –The kinds of adaptive changes that underlie tolerance and dependence are such that, once they have taken place, continued drug use is required for the brain to function “normally.” If drug use is stopped, the drug-adapted brain can no longer function properly, and withdrawal syndrome ensues. The withdrawal reaction continues until the adaptive changes have had time to revert, restoring the CNS to its pretreatment state.

Question 3

Tolerance

Answer 3

• –Tolerance and physical dependence are special manifestations of CNS adaptation. Tolerance is a decreased response occurring in the course of prolonged drug use.
• –The kinds of adaptive changes that underlie tolerance and dependence are such that, once they have taken place, continued drug use is required for the brain to function “normally.” If drug use is stopped, the drug-adapted brain can no longer function properly, and withdrawal syndrome ensues. The withdrawal reaction continues until the adaptive changes have had time to revert, restoring the CNS to its pretreatment state.