Pharmacokinetics

Question 1

Define Pharmacokinetics

Answer 1

What the body does to a drug.
It has four properties which are:
Absorption= transfer of drug from the site of administration to the bloodstream

Distribution
Metabolism
Elimination

Question 2

Define Pharmacodynamics

Answer 2

This what the drug does to the body

Question 3

What are the routes of drug administration

Answer 3

Enteral=oral, sublingual, transbuccal, intraduodenal

Parental= intravenously, Subcutaneous, intramuscular, oral inhalation, nasal inhalation ,

Question 4

Define Absorption

Describe the mechanism of absorption of drugs from the GI tract

Answer 4

drug into the blood plasma, during this stage the drug crosses the cell membranes

Passive diffusion= Drug moves toward the concentration gradient, from a high concentration to a lower concentration. This is namely lipid soluble drugs.

Facilitated Diffusion=Drug enters the cell via drug transporters from an area of an high concentration to a low concentration. this process does not require ATP
Active transport= Carrier proteins are used to transfer bigger molecules such as sugar, ions, aminoacids, pyrimidines. This process works against the concentration gradients and uses ATP

Endocytosis/Pinoytosis= involves engulfment of a drug molecule by the cell membrane and transport into the cell by pinching off the drug to form vesicle. B12 is an example of this. This is for larger molecules

Exocytosis= The cell secretes the vesicle out of the cell. For larger molecules

Question 5

Define Distribution

Answer 5

Drug leaves the blood stream and enters the extracellular fluids and then the tissues

Question 6

Define Elimination

Answer 6

Inactivation +Excretion of the drug from the body

Question 7

Describe first-pass metabolism

Answer 7

This is when the drug is administered orally and passes through the liver, when some of the drug is metabolised first before reaching the rest of the body . This does not happen with IV medications.

Question 8

List the factors influencing absorption

Answer 8

1 Chemical structure
2 water/lipid-soluble
3 pH of drug
4 route of administration
5 type of medication 
6 Blood flow to the absorption site
7 The surface area of the absorption site
8 Contact time at the absorption site 
9 Bioavailability

Question 9

Define Bioavailability

Answer 9

The amount of administered drug which enters the systemic circulation

Question 10

Why is it important to understand the drug Bioavailability

Answer 10

This is to calculate the drug dosage for intravenous routes

Calculation= Oral intake/ Iv intake * 100

Question 11

List the factors affecting bioavailability

Answer 11

1 First-pass hepatic metabolism

2 Chemical instability

3 Solubility of the drug

4 Nature of the drug formulation

Question 12

Factors influencing distribution

Answer 12

1 Blood flow to the tissues, is due to the unequal distribution of the cardiac output. Such organs with high blood flow are the brain, kidneys and liver.

2 Capillary permeability, in the brain, the capillaries of the blood-brain barrier, are closely fused together, this mean drugs cannot pass through. This is different compared to organs such as the liver and spleen where there is a higher capillary permeability.

3 Binding of plasma proteins and tissue proteins i.e Albumin this is reversible, however, slows down the process of drug distribution.

4 Hydrophobicity

Question 13

Define biotransformation/ metabolism

Answer 13

This is the process of detoxifying

breaking down the drug to become more polar so it can be removed from the system

Question 14

List the reactions of Phase 1 reaction

Describe the process of phase 1 drug metabolism

Answer 14

Oxidation, Reduction and hydrolysis reaction

These reactions are important as it converts hydrophobic compounds into more water-soluble (polar ) by adding a hydroxyl group O-H or amine group NH2 so that it can be excreted.

Hepatic cytochrome P450 system is very important in oxidation reaction

Oxidation reaction is the most common reaction

Question 15

Which organ primarily takes part in Phase 1 drug metabolism

Answer 15

Liver

Other organs include the kidneys, lungs, glands

Question 16

Describe phase 2 reaction

Answer 16

This is called a conjugation reaction, as the drug from phase 1 are still too lipophilic thus cannot pass through the kidneys, so reactions with endogenous substrate is needed.
Glucuronic acid, sulfuric acid , amino acids, methyl and acetyl

[Note: Drugs already possessing an –OH, –NH2, or –COOH group may enter Phase II directly and become conjugated without prior Phase I metabolism.] The highly polar drug conjugates may then be excreted by the kidney or in bile.

Question 17

Define excretion

Answer 17

This is the process by which the drug leaves the body

Question 18

List the different ways in which drugs are excreted

Answer 18

Urine
bile
breast milk
saliva
sweat glands 
air

Question 19

Outline the process of drug elimination

Which organ primarily involves the elimination of drugs

Answer 19

The kidneys are the main organ which eliminates drugs. The drug has to be ionised and polar so that the drug will remain in the kidneys and not reabsorbed in the distal tubules.

The drug enters the glomerular filtration passes through the proximal tubules ….

Question 20

Define half-life

Answer 20

This is the amount of time for the drug to reach half of its concentration

Question 21

Define clearance

Answer 21

The volume of plasma that is removed from the drug per a minute
calculated - drug metabolising and drug eliminated organs

Question 22

Define volume of distribution

Answer 22

theoretical volume that would be necessary to contain the total amount of an administered drug at the same concentration that it is observed in the blood plasma.[

Question 23

Define Stead y-state concentration

Answer 23

This is the plasma concentration of a multiple dosed or continuously infused drug when the drug will accumulate until-the amount adminis­tered per unit time is equal to the amount eliminated per unit time.