Drug Terms + Equations

Question 1

Ligand

Answer 1

A substance that is bound to a protein

Question 2

Affinity

Answer 2

The tendency (attraction) of a ligand to bind to its receptor

Question 3

Drug

Answer 3

A chemical that affects physiological function in a specific way

Question 4

Agonist

Answer 4

A ligand that binds to a receptor and alters receptor state, resulting in biological response

Mimics action of NT

Question 5

Antagonist

Answer 5

A drug that reduces the action of another drug by binding to (and therefore blocking) its receptor

Question 6

Partial agonist

Answer 6

An agonist that cannot elicit a large effect (hence partial)

Question 7

Efficacy

Answer 7

The ability of an agonist to activate a receptor and evoke a response

Question 8

Drug potency

Answer 8

An expression of the activity of a drug in terms of concentration/amount needed to have an effect

Drug A requires 0.2 conc to evoke a response compared to Drug B at 1.5 conc
Drug A more potent

Question 9

Drug selectivity

Answer 9

The affinity a drug has for its intended target to the exclusion of other (‘off’) targets

Greater selectivity of target = greater likelihood drug will evoke intended action

Greater selectivity of ‘off’ targets = adverse effects

Question 10

Dose

Answer 10

A specified quantity of drug administered once/at stated intervals

Can be relevant to body weight (mg/kg)

Question 11

k+1
A + R ⇌ AR
k-1

Answer 11

A - ligand
R - receptor
k+1 - association (forward) rate constant
k-1 - disassociation (backward) rate constant

Question 12

PAR = [A]/ KA + [A]

Answer 12

Lower KA = greater affinity of ligand for receptor

KA = disassociation equilibrium constant = conc of ligand required to occupy 50% of receptors

Question 13

Competitive antagonism

Answer 13

Antagonist competes with agonist for the SAME binding site on receptor

Reversible, concentration-response curve shifted to right

Question 14

Non-competitive antagonism

Answer 14

Antagonist binds to separate site on the receptor

Receptor only active when agonist is bound alone

Action is reversible or irreversible

Question 15

Chemical antagonism

Answer 15

Antagonist combines in solution directly with the chemical being antagonised

(eg. Chelating agents, used to treat lead poisoning, bind to heavy metals and form a less toxic chelate)

Question 16

Physiological antagonism

Answer 16

Two agonists that produce opposite physiological actions cancel each other out

Question 17

Pharmacokinetic antagonism

Answer 17

The ‘antagonist’ reduces conc of active drug at its site of action

Question 18

Pharmacodynamics

Answer 18

What a drug does to the body

Affinity, potency, efficacy

Question 19

Pharmacokinetics

Answer 19

What the body does to a drug

Apparent volume of distribution, elimination half-life, clearance, bioavailability

Question 20

What can a drug be eliminated through

Answer 20

Urine, faeces, milk, sweat, expired air

Question 21

What method of drug administration avoids first pass metabolism

Answer 21

IV - straight into blood circulation

Question 22

Emax

Answer 22

The concentration of a drug that gives 100% maximal response

Question 23

EC50

Answer 23

The concentration of a drug that gives 50% maximal response

Question 24

Absorption

Answer 24

Drug is absorbed from site of administration - entry into plasma

Question 25

Distribution

Answer 25

Drug leaves bloodstream and is distributed into interstitial + intracellular fluids

Question 26

Metabolism

Answer 26

Drug transformation by metabolism by liver

Question 27

Excretion

Answer 27

Drug and/or drug metabolites excreted in urine, faeces or bile

Question 28

Ways in which drugs can cross cell membranes

Answer 28

Passive diffusion Facilitated diffusion Active transport Endocytosis

Question 29

Passive diffusion

Answer 29

Drug moves directly through lipids in the cell membrane

Question 30

Facilitated diffusion

Answer 30

Drug moves across cell membrane via carrier proteins - conformational change occurs Doesn’t need ATP Requires concentration gradient

Question 31

Active transport

Answer 31

Drug moves across cell membrane via carrier proteins Requires ATP Moves against concentration gradient

Question 32

Endocytosis

Answer 32

Invagination of part of the cell membrane. Drug is encased in a small vesicle then released inside the cell

Question 33

Apparent volume of distribution (Vd)

Answer 33

The extent to which a drug partitions between the plasma and tissue compartments Vd = dose/[drug]plasma

Question 34

As Vd increases, drug plasma concentration …

Answer 34

Decreases And vice versa

Question 35

Metabolism in the liver …. the bioavailability of drugs when administered orally

Answer 35

Reduces

Question 36

Bioavailability (F)

Answer 36

The amount of drug that eventually reaches systemic circulation F = quantity of drug reaching systemic circulation/dose 100% for IV

Question 37

Cmax and Tmax

Answer 37

The peak or maximum drug plasma concentration (Cmax), and the time when it occurs (Tmax)

Question 38

Clearance (CL)

Answer 38

The volume of blood removed (or cleared) of drugs when administered per unit of time CL= rate of drug elimination/[D]plasma

Question 39

First order kinetics

Answer 39

Rate of drug elimination increases as plasma drug concentration increases

Question 40

Vmax

Answer 40

Maximum rate of drug elimination

Question 41

Km

Answer 41

Drug concentration at which rate of elimination is 1/2Vmax

Question 42

[Drug]plasma

Answer 42

The drug concentration in plasma

Question 43

Steady state

Answer 43

Rate of drug administration = rate of drug elimination Input = output

Question 44

Dosage rate =

Answer 44

[Drug]plasma X CL

Question 45

t1/2 =

Answer 45

(0.693 X Vd)/CL

Question 46

How many half lives are required to reach steady state

Answer 46

5

Question 47

What is elimination half life (t1/2)

Answer 47

Determines how much time is required for drug to be eliminated from body

Question 48

MLCK

Answer 48

Responsible for smooth muscle contraction