Pharmacodynamics

Question 1

Ligand

Answer 1

molec that binds a receptor

Question 2

Receptor

Answer 2

• Specific molecule that a ligand binds to in order to change function of a system
• The interaction of ligand w receptor initiates action of the drug

Question 3

Effector

Answer 3

molec that translates receptor activity into a change in cellular activity . Receptor can also be an effector or modulate an enzyme downstream

Question 4

Agonist

Answer 4

Ligand that binds to receptor and produces maximal effect (includes endogenous ligands and activating drugs)

Question 5

Antagonist

Answer 5

Ligand that binds to receptor but doesn’t produce an effect itself and interferes with agonist activity.

Question 6

Inverse Agonist

Answer 6

• Drug that binds to the same receptor as an agonist but induces a pharmacological response opposite to that of the agonist
• Inverse agonists have opposite actions to those of agonists but the effects of both of these can be blocked by antagonists.

Question 7

Partial agonist

Answer 7

• Ligand binds to receptor but doesn’t produce max effect (action is dependent on system)
• A partial agonist produces less than the full agonist effect, even when it has saturated the receptors because it can bind to the inactive conformation of the receptor. In the presence of a full agonist, a partial agonist competes for binding, so a partial agonist can act as a partial antagonist

Question 8

Competitive antagonist

Answer 8

A drug or chemical which binds to a specific receptor site and once there, blocks another drug or chemical from binding to that site. While the competitive antagonist binds to a particular drug receptor site, another drug must compete to gain access to that receptor.

drug directly competes with binding of an antagonist to the receptor. Because the antagonism is competitive, the presence of antagonist increases the agonist concentration required for degree of response, and so the agonist concentration-effect curve is shifted to the right.

Question 9

Non-competitive antagonist

Answer 9

the curve is shifted to the right. Maximal responsiveness is preserved, however, because the remaining available receptors are still in excess of the number required.

• EC50 increases

Question 10

Therapeutic Index

Answer 10

ratio of TD50 to ED50 to achieve some therapeutically relevant effect. High TI means that the drug is safer

Question 11

Therapeutic window

Answer 11

Range between minimum toxic dose and minimum therapeutic dose

Question 12

If a patient is suffering from bradycardia (low heart rate) due to excess signaling through muscarinic acetylcholine receptors, two treatments would be effective. One is to add a drug that binds and inhibits the muscarinic acetylcholine receptor (i.e. atropine) and another is to add a drug that excites the norepinephrine receptor (i.e. epinephrine). If epinephrine is used, its action in the context of the muscarinic acetylcholine receptor effect would be defined as which of the following?

Answer 12

physiological antagonist

** A physiological antagonist is when 2 drugs produce opposite effects on the same system or a drug opposes the effects of a natural signal molecule and reverses the effect of it (e.g. epinephrine in the treatment of histamine-induced broncospasm)

Question 13

A physiological antagonist is different from a receptor antagonist because its antagonist action is through which of the following mechanisms?

Answer 13

Objective 5: A physiological antagonist drug counters the effects of another by binding to a different receptor and causing opposing effects. If it competed for the same receptor, it would be a receptor antagonist (competitive or noncompetitive).

Question 14

Many types of receptors activate enzyme activity in response to ligand binding. In this context, the enzyme that becomes activated by the receptor is defined by which of the following terms?

Answer 14

Effector

• Objective 1; An effector is the component of a system that accomplishes the biologic effect after the receptor is activated by an agonist; often a channel, transporter, or enzyme molecule, may be part of the receptor molecule.

Question 15

A receptor ligand that has full agonist potency yet submaximal efficacy would be considered which of the following?

Answer 15

Partial agonist

• Objective 2; A partial agonist produces less than the full effect, even when it has saturated the receptors, possibly by combining with both receptor conformations, but favoring the active state. In the presence of a full agonist, a partial agonist acts as an inhibitor (i.e. partial antagonist).

Question 16

An inverse agonist produces a negative effect on receptor activity in the absence of agonist because the receptor has which of the following properties?

Answer 16

Constitutive activity

• Objective 2; Many receptors have some activity in the absence of agonist, referred to as constitutive activity. An inverse agonist is a drug that binds to the non-active state of receptor molecules and decreases constitutive activity. It is not a property defined by receptor subtype or number.

Question 17

In a graded dose-response relationship, the EC50 of a drug represents which of the following?

Answer 17

the dose that produces half-maximal effect

• Objective 1; As shown in the diagram, the EC50 is the concentration of drug that produces 50% of maximal effect. Emax is the maximal response that can be produced by the drug.

Question 18

In a quantal dose-response relationship, half-maximal effective dose ( ED50) refers to which of the following values?

Answer 18

The median dose that achieves 50% response in a population

• Objective 4; In quantal dose-response curves, the ED50 is the median dose that causes a specified response in 50% of the population under study. These curves are often used for determining safety of a drug.

Question 19

What is a characteristic of competitive binding?

Answer 19

shifted the EC50 to the right but not affected the Emax,

Question 20

A molecule binds to a receptor at a different site than the endogenous ligand. The binding of the molecule causes inhibition of binding by the endogenous ligand. The molecule is considered a non-competitive antagonist for which of the following reasons?

Answer 20

A noncompetitive antagonist will cause a reduction in Emax because the receptors are not available for the ligand to bind. A physiological antagonist by definition affects a different receptor