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