W2: Mechanism of drug absorption

Question 1

The degree of ________ AKA polarity is a factor affecting drug absorption. It is determined by the _____ of the drug and pH of the _____.

Answer 1

Degree of ioinization determined by the pKa of a drug and the pH of the media (biological fluids)

Question 2

What are the factors affecting drug absorption?

Answer 2

1. Surface area at site of administration
2. Aqueous solubility of the drug
3. route of administration
4. Vascularity of the absorbing surface
5. concentration

Question 3

Acidic drug absorbs better in ______ media, similarly, basic drug has better absorption in _____ media.

Answer 3

acidic drug in acidic media

Basic drug in basic media

Question 4

Talking about polarity, ______ drugs have a higher rate of absorption than _______ drugs because they can diffuse across _______.

Answer 4

Non-polar drugs have higher rate of absorption than polar drugs because it can diffuse across cell membrane easily.

Polar drugs rely on different mechanism of transport for drug absorption

Question 5

How does aqueous solubility affect drug absorption?

Answer 5

The rate of absorption depends on the rate of dissolution. Liquid absorption is faster than solid.

Question 6

Passive diffusion depends on ______________.

Answer 6

concentration gradient

Question 7

What are the two ways drug can move across cell membrane?

Answer 7

Bulk flow transfer = from bloodstream to cell, due to pressure gradient

Diffusion transfer = molecule to another molecule, due to concentration gradient

Question 8

Most of the drugs are ____ acid and bases hence the degree of ionization depends on the ________.

Answer 8

drugs are WEAK acid and bases hence the degree of ionization depends on the pH of the ENVIRONMENT.

Question 9

How can we increase the lipid solubility of a drug?

Answer 9

By either decreasing the ionization or adding a lipophilic group

Question 10

How can we increase the water solubility of a drug?

Answer 10

By ionization, adding a hydroxyl, carboxyl or amino group

Question 11

Most drugs are __________ in water.

Answer 11

partially ionized

Question 12

Aspirin is a weak acid of pKa 3.5, how will the increase of environmental pH affect the absorption of aspirin?

Answer 12

Aspirin is a weak acid and it tends to ionize (give up a H atom) in an aqueous medium at high pH. Drugs do not cross biological membranes when they are ionized. In a low pH environment like the stomach (pH =2), aspirin is predominantly unionized and crosses membranes into the blood vessels readily.

Question 13

Okay, how can we cross the damn cell membrane? List the ways we can cross as drugs.

Answer 13

1. Passive diffusion = if you are lipid soluble, depend on concentration gradient, non saturable, no ATP, carrier protein or protein channel
2. Filtration = occurs via pores of membrane or paracellular spaces, depend on osmotic pressure. IF you ain’t lipid soluble but smaller than the pores, then you can cross.
3. Active transport = against concentration gradient, need ATP, saturation occurs, can be inhibited
4. Facilitated diffusion = for monosaccharides, amino acids and vitamins. No need ATP, structure specific, saturable*, uses carrier proteins, can be inhibited
5. Endocytosis (objects) or pinocytosis (fluids)

Question 14

Transmembrane proteins are ________ or transporters. What are some of their characteristics?

Answer 14

Transmembrane proteins are carriers or transporters.

They are substrate specific, can undergo conformational change, need to use ATP, works slowly

Question 15

Transmembrane can be competitively inhibited by ________ which utilize the same transporter.

Answer 15

inhibit by antagonist / analogue

Question 16

Modified release dosage will affect the bioavailability of a drug. What are the types of release dosage?

Answer 16

Slow release = where the medication is designed to to be released slowly over time

Intermediate release = formulated to release the active drug immediately after oral administration. No active changed were made to the drug.