Flashcards in USMLE Gen Pharm Deck (426)
Km = Substrate at 0.5*Vmax
Km reflects the affinity of the enzyme for its substrate
Vmax indicates what?
Vmax is directly proportional to the enzyme concentration.
Relationship between Km and affinity
–The lower the Km, the higher the affinity
–Smaller Km means enzyme is saturated earlier, which means that small amounts of substrate are picked up by the enzyme.
Reading an inverse curve: Y–intercept equals ?
The higher the Y–intercept the lower the Vmax
Reading an inverse curve: X–intercept equals ?
The further to the right the x–intercept, the greater the Km
Reading an inverse curve: Slope equals ?
Reading an inverse curve: Effect of a competitive inhibitor
X–intercept farther to the right, meaning Km is greater, because you need more substrate to get the same effect as the competitive inhibitor is hogging the enzyme.
The y–intercept is the same, meaning Vmax hasn't changed, because there isn't any more enzyme.
The slope is greater, because Km has increased while Vmax has stayed the same.
Reading an inverse curve: Effect of a noncompetitive inhibitor
The x–intercept is the same, meaning Km is the same, because the affinity for the enzyme hasn't changed, there's just less of it.
The y intercept has increased, meaning Vmax has decreased, because enzyme has been inactivated by the noncompetitive inhibitor
The slope is greater, because Vmax has decreased while Km has stayed the same.
Competitive inhibitor: Resemble substrate
Competitive inhibitor: Overcome by increased substrate?
Competitive inhibitor: Binds active site?
Competitive inhibitor: Effect on Vmax
Unchanged. The amount of enzyme has not changed.
Competitive inhibitor: Effect on Km
Increased. A lot more substrate needs to be available to seize the active sites.
Noncompetitive inhibitor: Resemble substrate?
Noncompetitive inhibitor: Overcome by increased substrate?
Noncompetitive inhibitor: Binds active site?
Noncompetitive inhibitor: Effect on Vmax
Decreased. Takes the enzyme out.
Noncompetitive inhibitor: Effect on Km
Unchanged. Does not change the affinity for the enzyme.
Volume of distribution: Abbreviation
Vd: Stands for what?
Volume of distribution
Volume of distribution: definition
Vd = (amount of drug in the body)/(plasma drug concentration)
Volume of distribution: What alters it?
Liver and kidney disease
Where are drugs with a low Vd distributed?
Where are drugs with a medium Vd distributed?
Where are drugs with a high Vd distributed?
(rate of elimination of drug)/(plasma drug concentration)
=Vd x Ke where Ke=elimination constant
Half life: definition
The time required to change the amount of drug in the body by 1/2 during elimination (or during a constant infusion).
What percentage of steady state is a drug at after: 1 half life
What percentage of steady state is a drug at after: 2 half lives