Absorption and Distribution

Question 1

What routes can a drug take to cross the blood-brain barrier?

Answer 1

• lipid-soluble diffusion

- carrier-mediated

Question 2

What is the Henderson-Hasselbach Equation?

Answer 2

pH = pKa + log [unprotonated] / [protonated]

Question 3

Which form of a drug predominates if the pH is greater than its pK?

Answer 3

The unprotonated form predominates

Question 4

If you have a concentration of an uncharged drug on one side of a membrane, what will its concentration be on the other side of the membrane?

Answer 4

Uncharged drug diffuses freely and will be equal in concentration on each side of a membrane

Question 5

Weak acid such as phenobarbital (pKa 7.2) –

Will it be better absorbed from the stomach or colon?

Answer 5

Stomach

-the pH is much lower than pK, so most of the drug is unionized and hydrophobic

Question 6

In general, if a weak acid is protonated, is it charged or neutral?

Answer 6

neutral

Question 7

In general, if a weak base is protonated, is it charged or neutral?

Answer 7

Charged

Question 8

When does an ion get trapped (ion trapping)?

Answer 8

• when pKa of a drug is between the pH of 2 compartments

- drug gets trapped on the side with the higher ionized fraction

Question 9

What is the difference between Enteral and Parenteral routes of drug administration?

Answer 9

• Enteral = absorbed from G.I. tract

- Parenteral = bypasses the GI tract

Question 10

Which Enteral administration routes bypass the liver?

Answer 10

• sub-lingual

- Rectal (50% bypasses liver)

Question 11

Are inhalers considered enteral or parenteral?

Answer 11

parenteral

Question 12

What is the bioavailability of a drug?

Answer 12

-a comparison of the total amount of drug available to the body after a dose administered by some other route than intravenous

Question 13

What is the formula for volume of distrubution (Vd)?

Answer 13

Vd = Dose of drug / plasma concentration of drug