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Flashcards in Pharma - Pharmacodynamics Deck (66)
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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?

Four

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