Pharmacology - Pharmacodynamics Flashcards Preview

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Flashcards in Pharmacology - Pharmacodynamics Deck (60):
1

In enzyme kinetics, competitive inhibitors _____ (resemble/do not resemble) the substrate while noncompetitive inhibitors _____ (resemble/do not resemble) the substrate.

Resemble; do not resemble

2

In enzyme kinetics, the value of Km reflects the _____ of the enzyme for its substrate.

Affinity

3

True or False? In enzyme kinetics, the lower the Km, the higher the affinity.

True

4

In enzyme kinetics, Vmax is directly proportional to the _____ _____.

Enzyme concentration

5

In enzyme kinetics, a graph of substrate concentration on the x-axis and velocity of the reaction on the y-axis has _____ (increasing/decreasing) velocity as substrate is increased.

Increasing, although it will plateau when the enzyme is saturated

6

When velocity is equal to one half of its maximum (Vmax), the corresponding concentration of substrate is equal to what value?

Km

7

In enzyme kinetics, the y-intercept of a graph that plots the inverse of velocity on the y-axis and the inverse of substrate concentration on the x-axis is equal to what value?

The inverse of Vmax = 1/Vmax

8

In enzyme kinetics, the x-intercept of a graph that plots the inverse of velocity on the y-axis and the inverse of substrate concentration on the x-axis is equal to what value?

The inverse of Km= 1/Km

9

In enzyme kinetics, the slope of a graph that plots the inverse of velocity on the y-axis and the inverse of substrate concentration on the x-axis is equal to what value?

Km/Vmax

10

In enzyme kinetics, a competitive inhibitor _____ (cannot/can) be overcome by increasing the concentration of substrate; a noncompetitive inhibitor _____ (cannot/can) be overcome by increasing the concentration of substrate.

Can; cannot. This is because competitive inhibitors bind the active site of the enzyme, competing with the substrate, whereas noncompetitive inhibitors bind elsewhere on the enzyme and so are not affected by substrate concentration

11

In enzyme kinetics, competitive inhibitors _____ (increase/decrease/do not change) the Vmax of the reaction, while noncompetitive inhibitors _____ (increase/decrease/do not change the Vmax of the reaction.

Do not change; decrease

12

In enzyme kinetics, competitive inhibitors _____ (increase/decrease/do not change) the Km of the reaction, while noncompetitive inhibitors _____ (increase/decrease/do not change the Km of the reaction.

Increase; do not change

13

What is the formula for calculating the volume of distribution of a drug?

Volume of distribution = amount of drug in the body / plasma drug concentration

14

Drugs with a low volume of distribution, such as 4-8 L, are found in the _____ (blood/extracellular space/tissues).

Blood alone; these drugs do not distribute outside the plasma

15

A drug with a volume of distribution of 15 L is most likely to be found in the _____ (blood/extracellular space/tissues).

Extracellular space; these drugs distribute throughout the total body water

16

In a 75 kg man, a drug has a volume of distribution of 40 L. It can be expected to be found in _____ (blood/extracellular space/tissues).

Tissues

17

What is the formula for calculating the clearance of a drug?

Clearance (L/min) = rate of elimination of drug (g/min) / plasma drug concentration (g/L)

18

What is the definition of the half-life of a drug?

The time required to reduce the amount of drug in the body by one half

19

How many half-lives of a drug must pass before a drug infused at a constant rate reaches approximately 94% of steady-state concentration?

4

20

Given the volume of distribution and clearance of a drug, how does one calculate the half-life of the drug?

Half-life = (0.7 × volume of distribution) / clearance

21

After one half-life, given constant intravenous infusion of a drug, how close to steady-state is the concentration of the drug?

50% of steady-state concentration

22

After three half-lives, given constant intravenous infusion of a drug, how close to steady-state is the concentration of the drug?

87.5% of steady-state concentration

23

What is the formula for the loading dose of a drug?

Loading dose = (target plasma concentration × volume of distribution) / bioavailability

24

What is the formula for maintenance dose of a drug administered intravenously?

Maintenance dose = rate of elimination/bioavailability = (target plasma concentration × clearance) / bioavailability

25

How do loading and maintenance doses of drugs differ for patients with hepatic and renal disease?

For both hepatic and renal disease, loading dose does not change, but maintenance dose decreases

26

What is the bioavailability of a drug if it is administered intravenously?

100%

27

In zero-order elimination of drugs from the body, what is the relationship between the rate of elimination and the drug concentration?

The rate of elimination is constant regardless of drug concentration

28

What are three drugs that exhibit zero-order elimination?

Phenytoin and ethanol; aspirin at toxic concentrations

29

In first-order elimination of drugs from the body, what is the relationship between the rate of elimination and the drug concentration?

The rate of elimination is directly proportional to the drug concentration; a constant fraction (rather than a constant amount) is eliminated

30

In zero-order elimination of drugs from the body, how does the plasma concentration of a drug change over time: linearly or exponentially?

Linearly

31

In first-order elimination of drugs from the body, how does the plasma concentration of a drug change over time: linearly or exponentially?

Exponentially

32

Weak acids get trapped in _____ (acidic/basic) environments.

Basic

33

Weak bases get trapped in _____ (acidic/basic) environments.

Acidic

34

What substance is given to enhance the renal clearance of weakly acidic drugs such as phenobarbital, methotrexate, and aspirin?

Bicarbonate

35

What substance is given to enhance the renal clearance of weakly basic drugs such as amphetamine?

Ammonium chloride

36

Ionized species become trapped in urine because they are not _____ _____.

Lipid soluble; therefore, they cannot cross cell membranes

37

A 24-year-old man attempts suicide by consuming a small bottle of aspirin. After three hours he thinks better of it, and comes to the emergency room. He is put in your care, and you start him on intravenous saline with bicarbonate. By what mechanism does this help him?

Bicarbonate alkalinizes the lumen of his nephrons, which traps acetylsalicylic acid within the lumen because it is a weak acid and is ionized in a basic environment

38

What three types of biochemical reactions are involved in the phase I metabolism of drugs?

Reduction, oxidation, and hydrolysis

39

What is the polarity of the drug products that result from phase I metabolism?

The products are slightly polar

40

True or False? Drug products that result from phase I metabolism are water soluble.

True

41

True or False? Drug products that result from phase I metabolism are often still active.

True

42

What enzyme system mediates the phase I metabolism of drugs in the body?

Cytochrome P-450

43

What three types of biochemical reactions are involved in the phase II metabolism of drugs?

Acetylation, glucuronidation, and sulfation; these are conjugation reactions

44

Do geriatric patients lose the ability for phase I or phase II drug metabolism first?

Phase I

45

Phase I metabolism of drugs yields _____ (nonpolar/slightly polar/very polar) molecules that are _____ (inactive/often still active), whereas phase II metabolism of drugs yields _____ (nonpolar/slightly polar/very polar) molecules that are _____ (inactive/often still active).

Slightly polar; often still active; very polar; inactive

46

The products of phase II metabolism of drugs are excreted by what organ?

Kidneys

47

What is the definition of efficacy?

Maximal effect a drug can produce

48

What is the definition of potency?

Amount of drug needed for a given effect

49

A drug that requires a very low dose to achieve its desired effect is considered _____.

Potent

50

True or False? In pharmacodynamics, when a competitive antagonist is given, the maximal effect of an agonist is decreased regardless of how much additional agonist is given.

False; the maximal effect of an agonist is still achievable in the presence of a competitive antagonist if increased amounts of the agonist are given

51

What is the effect of a noncompetitive antagonist on the position of an agonist's dose-response curve?

It vertically shrinks; the agonist's efficacy is decreased

52

In pharmacodynamics, the addition of a noncompetitive agonist _____ (increases/decreases/does not change) the efficacy of the agonist.

Decreases

53

How does the efficacy of a partial agonist relate to the efficacy of a full agonist of the same receptor?

A partial agonist has a lower maximal efficacy than a full agonist

54

How does the potency of a partial agonist relate to the potency of a full agonist of the same receptor?

A partial agonist may be more potent than, less potent than, or equally as potent as a full agonist

55

What property of a drug is determined by its therapeutic index?

Safety; drugs with higher therapeutic indices are less likely to cause toxicities

56

What is the formula that describes the therapeutic index of a drug?

TI (therapeutic index) = LD50(median toxic dose) / ED50(median effective dose) (remember: TILE)

57

Safer drugs have _____ (higher/lower) therapeutic index values.

Higher

58

Competitive inhibitors ____ (decrease/do not change) the Vmaxof a reaction; noncompetitive inhibitors ____ (decrease/do not change) Vmax.

Do not change; decrease

59

Competitive inhibitors ____ (increase/decrease) the Km of a reaction; noncompetitive inhibitors ____ (decrease/do not change) the Km.

Increase; do not change

60

Morphine and buprenorphine are agonists at the same receptor, so why are their effects different?

Partial and full agonists act at the same receptor site but with reduced maximal effect

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