Pharmacodynamics Flashcards
What is the relationship between Km & affinity that an enzyme has for a substrate?
Km & affinity are inverses of each other.
What does the Km reflect and how is it reflected on a velocity vs substrate graph?
Km reflects the affinity of an enzyme for its substrate and is equal to the substrate level at 1/2 Vmax.
What is Vmax and how does it relate to the enzyme concentration?
Vmax is the maximum initial rate of a reaction. It is directly proportional to the enzyme concentration.
Compare Competitive inhibitors and Noncompetitive inhibitors in regards to: Resemble substrate? Overcome by increasing the substrate? Bind the active site? Effect on Vmax? Effect on Km? Pharmacodynamics?
Competitive inhibitors Resemble substrate? Yes Overcome by increasing the substrate? Yes Bind the active site? Yes Effect on Vmax? None Effect on Km? Increased Pharmacodynamics? Decreases potency
Noncompetitive inhibitors: Resemble substrate? No Overcome by increasing the substrate? No Bind the active site? No Effect on Vmax? decreased Effect on Km? Unchanged Pharmacodynamics? Decreases efficacy
On a graph of 1/V on y-axis and 1/s on x-axis, how is the line of a Noncompetitive inhibitor vs a competitive inhibitor?
On a graph of 1/V on y-axis and 1/s on x-axis, the line of a Noncompetitive inhibitor is at a higher 1/v (lower Vmax)
On a graph of 1/V on y-axis and 1/s on x-axis, the line of a competitive inhibitor
What is the Vd? How is it calculated? What factors may affect it?
Vd is the volume distribution of the drug. It relates the amount of drug in the body to the plasm concentration. The volume distribution of a Protein-bound drugs can be altered by liver and kidney disease which will decrease plasma protein binding and therefore increase Vd.
Give an example and characteristic of a drug with a low Vd (4-8 L)?
A drug with a low Vd is largely distributed in the blood. It is usually large or charged. Ex: warfarin and aspirin are basic drugs.
Give an example and characteristic of a drug with a medium Vd?
A drug with medium Vd distribute in the extra cellular space or body water. They are small hydrophilic molecules that do NOT bind plasma proteins.
Give an example and characteristic of a drug with a large Vd?
A drug with a high Vd (higher than body weight) distributes in all tissues. It is a drug that is small, lipophilic that can bind strongly to extravascular proteins. Ex: amphetamine which is a basic drug.
What is clearance pertaining to and what two ways can it be calculated?
Clearance relates the rate of elimination of a drug to the plasma concentration of the drug.
1- CL = rate of elimination of the drug/plasma concentration of the drug.
2- CL = Vd x Ke
Ke is the elimination constant of the drug.
What is does the half life of a drug pertain to ?
T1/2 is the time required to change the amount of drug in the body by 1/2 during elimination or constant infusion. It is a property of First order elimination in which the same Fraction of the drug is eliminated.
A drug infused at a constant rate with first order elimination takes how many half lives to reach steady state?
A drug with first order elimination infused constantly takes 4-5 half lives to reach constant state.
What is the formula for half life of a first order elimination drug?
T1/2 = (0.7 x Vd)/ CL
What is the bioavailability and what sign denotes it? How if the bioavailability via IV administration compared to oral?
Bioavailability is denoted by F, it is the fraction of administered drug that reaches circulation.
IV the F is 100%
Orally the F is the % that survives first pass in the liver or gut.
How is the loading dose calculated for a drug? How do renal or liver disease affect your loading dose?
Loading dose = (Cp x Vd)/F and in renal or liver disease the loading dose is not changed.
Cp is the target plasma concentration.
