Chapter 5: Pharmacodynamics

Question 1

Pharmacodynamics

Answer 1

The study of what drugs do to the body

Question 2

dose-response relationship

Answer 2

The relationship between the size of a dose and the intensity of the response.
Phase 1: Dose too low to elicit a response.
Phase 2: Dose increase elicits an increase in response.
Phase 3: Eventually a point is reached where an increase in dose is unable to elicit a further increase in response.

Question 3

maximal efficacy

Answer 3

The largest effect that a drug can produce.

Question 4

relative potency

Answer 4

The amount of drug we must give to elicit an effect.

Question 5

Receptors

Answer 5

A macromolecule in a cell to which a drug binds to produce an effect.
USUALLY reversible.
Drugs and receptors act as a lock-and-key mechanism.
Receptors can become desensitized with prolonged exposure to a drug.

Question 6

Single Occupancy Theory

Answer 6

1) Intensity is related to how many receptors a drug occupies
2) Maximum effect is achieved when all receptor have been occupied.

Question 7

Modified Occupancy Theory

Answer 7

1. affinity- the strength of attraction between a drug and its receptor. (Reflected in potency)
2. intrinsic activity- the ability of a drug to activate the receptor following binding (Reflected in maximal efficacy)

Question 8

Affinity

Answer 8

High affinity means strong drug attachment to receptors. The affinity of a drug is reflected in its potency. Drugs with high affinity are very potent.

Question 9

Intrinsic Activity

Answer 9

Refers to the ability of a drug to activate a receptor upon binding. Drugs with high intrinsic activity cause intense receptor activation.

Question 10

Agonists

Answer 10

Drugs that mimic the action of endogenous molecules. Activate receptors. It has both affinity and high intrinsic activity.

Question 11

Antagonists

Answer 11

1. Noncompetitive
2. Competitive (common)
   Drugs that block effects. Prevent molecules from binding. Have NO EFFECT OF THEIR OWN on the receptor.
   It has affinity but no intrinsic activity.
   Narcan (naloxone)

Question 12

Noncompetitive Antagonists

Answer 12

Irreversible.
Essentially reduces number of available receptors.
Effect will last until cell is recycled or drug is metabolized.

Question 13

Competitive Antagonists

Answer 13

REVERSIBLY.

If affinity is the same, drugs with higher concentrations will bind.

Question 14

Regulation of Receptor Sensitivity

Answer 14

The # of receptors on the cell can change, as can their sensitivity to agonist molecules. Continuous exposure to an agonist can make a cell become desensitized (refractory or undergone down-regulation). Continuous exposure to an antagonists can make a cell become hypersensitive (supersensitive).

Question 15

Therapeutic Index

Answer 15

A measure of a drug’s safety.
Defined as the ratio of a LD50 : ED50. (LD50 is the dose that is lethal to 50% and the ED50 is defined as the dose that is required to produce a therapeutic response in 50%)

Question 16

Dobutamine

Answer 16

A drug that mimics the action of the neurotransmitter norepinephrine (NE) and acts as an agonist.

Question 17

A low therapeutic index

Answer 17

A low therapeutic index (TI) indicates that the difference between the therapeutically active dose and the toxic dose of a drug is small. Therefore, a drug that has a low TI has a greater likelihood of toxicity relative to other drugs. There may be a high possibility of overdose with this drug.