How Drugs Work p2

Question 1

Drug distribution
1. What is it?
2. Goal of it?
3. Factors affecting it (4)

Answer 1

1. The physiological movement of drugs from the systemic circulation to the tissues.
2. To reach target tissue or intended site of action.
3. Factors affecting
   - Membrane permeability
   - Tissue perfusion
   - Protein binding
   - Volume of distribution

Question 2

Membrane permeability is where drugs must pass through the “___” in the ___ to enter the tissues.
Certain capillary beds are “___” & do not allow may drugs to leave into tissues. The ___-___ ___, ___, ___, & ___ are all locations such as this.

Answer 2

1. “Windows”
2. Capillaries
3. “Tight”
4. Blood-brain barrier, Cornea, Prostate, & Placenta

Question 3

Perfusion effect is when drugs administered SQ & IM must diffuse through the ___ & enter capillaries to enter general ___.
The better the blood supply of the tissue, the more ___ uptake.

Answer 3

1. Tissues
2. Circulation
3. Rapid

Question 4

T/F: Animals that are in shock have poor perfusion and it is advised to avoid SQ injections due to their poor perfusion

Answer 4

True

Question 5

Protein binding:
Certain drugs attach to ___ & other proteins in the ___.
The more protein binding occurs with a drug, the ___ the dosage must be to distribute the drug to the ___.

Answer 5

1. Albumin
2. Plasma
3. Higher
4. Tissues

Question 6

T/F: Protein binding complex is small enough to fit through the capillary windows.

Answer 6

False.
It is too LARGE to pass thru the capillary windows!

Question 7

Volume Distribution
1. What is it?
2. Why is it important to know this?

Answer 7

1. Represents the number of tissues the drug gets into or the % of drug that leaves the blood to enter the tissues.
2. Important to know in obese vs lean animals of the same body weight.

Question 8

T/F: An obese animal should be given less drug based on their body weight according to volume distribution

Answer 8

True

Question 9

Answer 9

The patient who is more lean

Question 10

Biotransformation (metabolism)
1. What is it?
2. Primary site:

Answer 10

1. The chemical alteration of drug molecules by the body to metabolite that is in
   - Change to an activated form
   - An inactivated form
   - And/or a toxic form
2. The LIVER

Question 11

Biotransformation of the same drug may vary with… (3)

Answer 11

1. Species
2. Age
3. Health
   - Organ function

Question 12

What is drug elimination?

Answer 12

The movement of drugs out of the body

Question 13

Routes of drug elimination
1. Two major routes
2. Others (3)

Answer 13

1. Major
   - Liver (bile into feces)
   - Kidney (urine)
2. Others
   - Lungs
   - Skin (sweat)
   - Milk

Question 14

Withdrawal time, what is it?

Answer 14

Period of time after drug administration during which the animal cannot be sent to market for slaughter, eggs, or milk must be discarded because of the potential for drug residues.

Question 15

What is half-life?

Answer 15

Time required for the amount of drug in the body to be reduced by half of its original level.
- It takes 5 half-lives for a drug to clear the body

Question 16

What is a steady state?

Answer 16

Point at which drug accumulation & elimination are balanced