# Pharma - Pharmacodynamics Flashcards

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

Resemble; do not resemble

In enzyme kinetics, the value of K_{m} reflects the _____ of the enzyme for its substrate.

Affinity

True or False? In enzyme kinetics, the lower the K_{m}, the higher the affinity.

TRUE

In enzyme kinetics, V_{max} is directly proportional to the _____ _____.

Enzyme concentration

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

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

K_{m}

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 V_{max} = 1/V_{max}

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 K_{m} = 1/K_{m}

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?

K_{m}/V_{max}

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

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

Do not change; decrease

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

Increase; do not change

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

100%