Question

4 multiple answer 1 point
although barriers in the body, such as the blood - brain barrier and the placenta, protect the brain and developing fetus, respectively, some drugs can still cross these barriers. a number of drugs with different properties are shown below. which of these drugs are most likely to cross the blood - brain barrier? (select all that apply.)
high molecular weight drug
low molecular weight drug
water - soluble drug
fat - soluble drug
nonpolar drug
small drug
polar drug
5 multiple choice 1 point
chloramphenicol and gentamicin are both antibiotic drugs used to treat infection. chloramphenicol has a molecular weight of approximately 323 g/mol and is extremely fat - soluble. gentamicin has a molecular weight of approximately 477 g/mol and is extremely water - soluble. which of these drugs is most likely to cross the blood - brain barrier?
chloramphenicol
gentamicin

Explanation:

Question 4 (Multiple Answer)

The blood - brain barrier (BBB) is composed of lipid - rich cell membranes. For a drug to cross the BBB:

1. Molecular weight: Smaller (low molecular weight) and small - sized drugs can more easily pass through the narrow spaces or diffuse through the membrane compared to high - molecular - weight drugs.
2. Solubility: Fat - soluble (lipid - soluble) drugs can dissolve in the lipid - rich membranes of the BBB. Water - soluble drugs have difficulty crossing the lipid - based barrier.
3. Polarity: Nonpolar drugs can interact favorably with the nonpolar lipid environment of the BBB membranes. Polar drugs have a hard time crossing the nonpolar lipid - rich barrier.

So, low molecular weight drug, fat - soluble drug, nonpolar drug, and small drug are likely to cross the BBB. High molecular weight drugs (too big), water - soluble drugs (can't dissolve in lipid), and polar drugs (don't interact well with nonpolar lipid) are less likely.

To cross the blood - brain barrier, a drug should be fat - soluble (lipid - soluble) and have a relatively low molecular weight (small size). Chloramphenicol has a molecular weight of ~ 323 g/mol (lower than gentamicin's ~ 477 g/mol) and is extremely fat - soluble. Gentamicin is extremely water - soluble and has a higher molecular weight. So, chloramphenicol is more likely to cross the BBB.

Answer:

B. low molecular weight drug, D. fat - soluble drug, E. nonpolar drug, F. small drug

Question 5 (Multiple Choice)