International Board of Certified Lactation Consultant (IBCLC) Practice Exam

What characteristic do most drugs that work on the CNS exhibit?

1. High lipid solubility

2. Low molecular weight

3. High protein binding

4. Short half-lives

The correct answer is: High lipid solubility

Most drugs that work on the central nervous system (CNS) exhibit high lipid solubility, which is essential for their ability to cross the blood-brain barrier. The blood-brain barrier is a selective permeability barrier that protects the brain from potentially harmful substances while allowing necessary nutrients to pass through. Lipid solubility enables drugs to diffuse across cell membranes, which are primarily composed of lipids. Drugs with high lipid solubility can effectively enter the brain tissue where they exert their therapeutic effects, such as altering mood, perception, or cognition. This characteristic is fundamental in the development of CNS-active medications, as it allows for the accurate targeting of specific receptors and systems within the brain. While factors such as molecular weight, protein binding, and half-lives do influence drug distribution and action, they do not play as central a role in the ability of a drug to enter the CNS as lipid solubility does. Low molecular weight can contribute to CNS penetration, but it is not the defining characteristic. Similarly, high protein binding can limit the free drug available to cross into the brain, and short half-lives may affect the duration of action rather than the ability to cross the blood-brain barrier. Thus, high lipid solub