Pharmacodynamics

Question 1

Michaelis-Menten kinetics

Answer 1

hyperbolic

Km is inversely related to the affinity of the enzyme for its substrate (low Km = high affinity). Km=concentration of substrate at 1/2 Vmax

Vmax is directly proportional to the enzyme concentrations. Vmax is efficacy of a drug. Increase Vmax=increase efficacy (maximal effect a drug can produce)

Question 2

Lineweaver burk plot

Answer 2

increase on Y intercept –> lower Vmax
Further right on X intercept –> greater Km –> lower affinity

competitive inhibitors cross eachother
noncompetitive inhibitors do not

Question 3

Competitive inhibitors, reversible

Answer 3

leave Vmax unchanged
Increase Km and thus decrease affinity
overcome by increase in substrate concentration
decreased potency

Question 4

Competitive inhibitors, irreversible

Answer 4

Not overcome by substrate concentration rise
decreases Vmax
Unchanged Km
decreased efficacy

Question 5

Noncompetitive inhibitors

Answer 5

Does not resemble substrate, is not overcome by increase in substrate concentration, does not bind active site.

Decreases effect on Vmax
Leaves Km unchanged
decreases efficacy

Question 6

Volume of distribution

Answer 6

Theoretical volume occupied by the total amount of drug in the body relative to its plasma cocnentration

Vd= amount of drug in the body/ plasma drug concentration

Question 7

Clearance

Answer 7

CL= rate of elimination of drug/ plasma drug concetration = Vd x Kc

Kc=elimination constant

Question 8

Half life in first order elimination

Answer 8

T1/2=(0.7xVd )/CL

Question 9

Loading dose

Answer 9

= (Cp x Vd) / F

Cp= target plasma concentration at steady state
F=bioavailability

Question 10

Maintenance dose

Answer 10

= ( Cp x CL x t) / F

Cp= target plasma concentration at steady state
F=bioavailability
CL= clearance
t=dosage interval

Question 11

Permissive

Answer 11

presence of substance A is required for the full effects of substance B

Question 12

Synergistic

Answer 12

Effect of substance A and B together is greater than the sum of their individual effects

Question 13

Tachyphylactic

Answer 13

acute decrease in response to a drug after initial/repeated administration

Question 14

competitive antagonists

Answer 14

shift curve to right (decreased potency)

Question 15

noncompetitive antagonists

Answer 15

shift curve down (decreased efficacy)

Question 16

partial agonist (alone)

Answer 16

Shifts curve down (Decreased efficacy)

Question 17

zero order elimination

Answer 17

Rate of elimination is constant regardless of Cp

Cp decreases linearly

PEA- phenytoin, ethanol, aspirin

Question 18

First order elimination

Answer 18

rate is directly proportional to drug concentration

Cp decreases exponentially

flow dependent elimation

Question 19

Urine pH and drug elimination

Answer 19

ionized species - trapped in urine and eliminated

neutral forms - reabsorbed

Question 20

Drug metabolism: phase I

Answer 20

Reduction
Oxidation
Hydrolysis

cytochrome P-450 –> slightly polar water soluble metabolites

Question 21

Drug metabolism: phase II

Answer 21

Conjugation (methylation, glucuronidation, acetylation, sulfation) usually yields a very polar inactive metabolite (renally excreted)

Question 22

Potency of a drug

Answer 22

amount of drug needed for a drug effect

As EC50 decreases the potency increases and less drug is needed

EC=effective concenration

Question 23

Therapeutic index

Answer 23

drug safety measure

TD50/ED50 = median toxic dose/ median effective dose

therapeutic window = dosage range that can safely and effectively treat disease

high TI=safer