Pharmacokinetics

Question 1

What is the process of absorption?

Answer 1

-process by which the drug moves from the site of administration to the bloodstream

Question 2

What is the bioavailability of a drug?

Answer 2

-the rate and extent to which the active ingredient is absorbed and reaches the circulation

Question 3

What are I/V drugs availability?

Answer 3

100% or 1

Question 4

What is passive diffusion in the process of absorption?

Answer 4

-across a biological membrane for an area of high concentration to low concentration

Question 5

What is facilitated diffusion in the process of absorption?

Answer 5

-involves special carrier molecules in the biological membrane

Question 6

What is active transport in the process of absorption?

Answer 6

-a carrier molecule is required
-the cells expends energy actively to transport the substance

Question 7

What is physical transport in the process of absorption?

Answer 7

-pinocytosis cells engulf molecules

Question 8

What are lipophillic drugs?

Answer 8

-fat soluble
-given via oral route

Question 9

How are lipophillic drugs absorbed?

Answer 9

-have an affinity for fat so more likely to dissolve in the fatty content of the stomach
-then passes across cell membranes
-moves across gut wall easily
-most absorption occurs across small intestine

Question 10

What are hydrophilic drugs?

Answer 10

-readily dissolve in water and diffuse through fluid
-usually given parenterally

Question 11

How are hydrophilic drugs absorbed?

Answer 11

-they diffuse through fluid
-they are ionised and cannot easily pass across the cell membrane
-require active transport mechanisms to do this
-they are deposited in the ECF and diffuse through tissue fluids and capillary walls

Question 12

How are orally administered drugs absorbed?

Answer 12

-absorbed across the GI tract and transported in the hepatic portal vein to the liver
-drug undergoes metabolism in the liver, known as first pass effect

Question 13

What is the first pass effect?

Answer 13

-when the drug travels via the liver first, before they are distributed around the body
-since livers function is metabolism it may partially breakdown drug and inactivate it to some degree and reduce effectiveness

Question 14

What 4 factors affect drug absorption?

Answer 14

Formulation of drug = liquids absorbed faster than solids

Route of administration = parenteral faster than oral

Perfusion of site of administration = well perfumed tissues will result in faster absorption

Patients condition = vomiting, diarrhoea, GI disease, presence of food

Question 15

What is the process of distribution?

Answer 15

Interstitial fluid
-»
Blood plasma
-»
Tissues
-»
Receptors

Question 16

What is the distribution of drugs?

Answer 16

-the movement of the drug from the circulation into the body tissues
-most drugs target specific receptors on cells and tissues, they bind to these to exert their effect

Question 17

What affects the distribution of drugs?

Answer 17

-formulation of the drug
-plasma proteins
-tissue perfusion

Question 18

How does the formulation of the drug affect distribution?

Answer 18

-lipophillic drugs can cross the cell membranes easily and are retained longer in fat-containing tissues
-when in bloodstream drugs can pass through gaps between cells in the capillary wall
-the capillaries in the brain have no gaps in their walls meaning only lipophilic drugs can cross the blood brain barrier

Question 19

How does plasma proteins affect drugs distribution?

Answer 19

-many drugs bind to plasma proteins when they enter the bloodstream which means their absorption is slow and controlled as not all of the drug molecules are free to act on these animal tissues - these drugs remain in the plasma until the protein release them

Question 20

How do free drug affect distribution?

Answer 20

-they aren’t bound to plasma proteins so move from the bloodstream into tissues quickly as their is nothing preventing their movement
-they can diffuse across the capillary walls, whereas bound drugs cannot

Question 21

How does tissue perfusion affect drugs distribution?

Answer 21

-good blood supply to the tissues leads to faster and better distribution
-drugs will take longer to be delivered to other areas of the body that are less well perfused

Question 22

What is drug metabolism?

Answer 22

-the body’s ability to change a drug from the from in which it was administered into a form that can be eliminated from the body
-most metabolism occurs in the liver
-some are metabolised by kidneys, lungs and intestinal tract

Question 23

How are drugs metabolised in the liver?

Answer 23

-liver enzymes transform the drugs into water soluble metabolites for excretion of the urine
-liver makes enzymes that transform drugs into a from that is more easily excreted either in urine or bile

Question 24

What occurs in phase 1 of metabolism?

Answer 24

-enzyme act on the drug to produce a metabolite by adding a molecule

-may be:
Oxidation = adding 02
Reduction = adding H
Hydrolysis = adding H20

Question 25

What occurs in phase 2 of metabolism?

Answer 25

-the liver combines the metabolite with another molecule to make it more water soluble -not all drugs will undergo this stage

Question 26

What 4 factors affect drug metabolism?

Answer 26

-species -drug interaction -repeated drug exposure -liver function

Question 27

How do different species affect drug metabolism?

Answer 27

-different species differ in ability to metabolise drugs -cats cannot produce most glucuronide conjugates meaning they struggle to effectively metabolise several drugs that require phase 2

Question 28

How does drug interaction affect metabolism?

Answer 28

-if 2 drugs are administered that are both metabolised by the same liver enzymes then the liver may not be able to produce enough enzymes to metabolise both drugs effectively -this can delay the metabolism of one or both and lead to toxic side effects

Question 29

How does repeated drug exposure affect metablism?

Answer 29

-can lead to the liver producing increased levels of biotransforming enzymes which means that a drug the animal has been taking over a period of time will be metabolised more quickly

Question 30

What is bio transformation?

Answer 30

-when a drug which an animal has been taking over a period of time is metabolised quicker -the animal builds a tolerance to the drug -will require increase in dosage

Question 31

How does liver function affect drug metabolism?

Answer 31

-immature or impaired liver function means the animal is less able to metabolise drugs effectively -the dose may need to be reduced or an alternative drug used

Question 32

How are drugs excreted?

Answer 32

-kidney is the main organ of excretion -excreted via urine -usually fat soluble drugs are excreted by the liver as bile and passed in faeces -small amounts excreted via saliva, sebum, milk and respiratory tract

Question 33

What is renal excretion?

Answer 33

-drugs are filtered from the blood into the urine by the kidney -small molecules can be forced through into the bowman’s capsule by ultrafiltration -other drugs are actively secreted into urine in the PCT

Question 34

How does poor perfusion to the kidney or renal disease affect drug excretion?

Answer 34

-will lead to a reduction in drug excretion

Question 35

What is hepatic excretion?

Answer 35

-the liver eliminates some metabolised drugs in bile -the bile enters the small intestine where it eventually passes out in faeces

Question 36

What is entero-hepatic recycling?

Answer 36

this is a phenomenon where the GI microflora act on the bile containing the drug metabolites resulting in the drug being released and reabsorbed from the intestine thereby re-entering the circulation