Primer 10

Question 1

What are the symptoms of excess parasympathetic activation? Parasympathetic inactivation?

Answer 1

SLUDE BBB/ DUMBELLS excess

opposite effects for inactivation

Question 2

What drug reverses organophosphate poisoning?

Answer 2

pralidoxime

Question 3

What is “Vmax” in kinetics? Where would you find it on a velocity/ concentration (curved) graph?
Where would you find it on a linear graph?

Answer 3

• V max is the highest reaction velocity that can be achieved with a given amount of enzyme.
• Point at which the addition of substrate cannot increase the reaction speed because all enzymes are saturated.
• Point at which zero order kinetics is observed.

*1/Vmax is the y intercept on a linear graph, and the highest velocity achieved on a curved plot.

Question 4

What is “Km” in kinetics? Where would you find it on a velocity/ concentration (curved) graph?
Where would you find it on a linear graph?

Answer 4

• Km is the amount of substrate needed to reach half of a reactions maximum velocity
• It is representative of an enzymes affinity for a substrate. Low Km = high affinity because less substrate is needed to reach max reaction speed.

*1/-Km is the x intercept of a linear plot, and the [S] at 1/2Vmax on a curved plot.

Question 5

How does the addition of a competitive inhibitor effect Vmax/ Km?

Answer 5

• Competitive inhibitors can be overcome by the addition of substrate and therefore do not change Vmax.
• With the addition of a competitive inhibitor, only Km is increased (representing a decreased affinity due to blockage of the enzymes active site)
• No change Vmax, increase Km

Question 6

How does the addition of a noncompetitive inhibitor effect Vmax/ Km?

Answer 6

• Noncompetitive inhibitors irreversibly inactivate enzymes. They cannot be overcome by the addition of a substrate and therefore decrease Vmax.
• Because they do not bind the active site of an enzyme, they do NOT change Km.
• Noncompetitive: decrease in Vmax, no change Km

Question 7

PRACTICE THE CONCEPT-
On a linear enzyme kinetics plot, how would a decrease in enzyme affinity appear?
What causes a decrease in enzyme affinity?

*Note: linear plot = 1/V0 vs 1/Km (y vs x)

Answer 7

• decreased enzyme affinity= increased Km.
• Would appear as a RIGHT shift of a linear plot.
• caused by addition of a competitive inhibitor; would not be accompanied by a change in Vmax/ y intercept.

Question 8

Volume of distribution equation for a drug that is administered IV (100% bioavailable):

Answer 8

Vd= drug dose/ drug concentration

Question 9

Equation for drug clearance:

Answer 9

CL= elimination/ concentration
CL= K x Vd where K = 0.7/ t1/2
Therefore…… CL= (0.7 x Vd)/ t1/2

Question 10

Loading Dose Equation:

Answer 10

LD= Css x Vd / F

where F = bioavailability and can be disregarded for IV medications.

Question 11

Maintenance Dose Equation:

Answer 11

MD= Css x CL

Question 12

How many half lives does it take to eliminate a drug? To reach steady state?

Answer 12

-4 half lives eliminate a drug by 94%;
-The reverse can be said for Css.
94% of Css is reached when a drug has been appropriately administered for four half lives.