Pharmacodynamics

Question 1

What factors affect drug absorption?

Answer 1

• rate of dissolution
• surface area
• blood flow
• lipid solubility
• pH partitioning

Question 2

What is the most common membrane transport mechanism?

Answer 2

non-protein mediated transport (simple diffusion)

Question 3

Transmembrane distribution and excretion of weak acids as it relates to pH/pKa

Answer 3

Weak acids (like aspirin) can only cross membranes in their un-ionized form
- get trapped in basic compartments

Question 4

Transmembrane distribution and excretion of weak bases as it related to pH/pKa

Answer 4

Weak bases (like amphetamine) can only cross membranes in their un-ionized form
- get trapped in acidic compartments

Question 5

What is the role of protein binding on drug distribution?

Answer 5

theres a finite number of protein binding sites in the plasma, addition of new drug can displace a bound drug
- certain drugs are only bioactive if free, so there will be partial retention of drugs in vasculature

Question 6

What are the parenteral routes of administration?

Answer 6

• intravenous: most direct route, increased risk of adverse effects
• intramuscular: quick/easy admission, rapid absorption, painful, can cause nerve injury
• subQ: quick/easy admission, rapid absorption, painful

Question 7

describe the concept of biotransformation

Answer 7

Two phases of drug metabolism

• Phase 1: oxidation, reduction, hydrolysis
• Phase 2: conjugation

Question 8

What is the physiologic role of biotransformation as it relates to drug therapy?

Answer 8

products are usually more polar metabolites

- oxidative processes often involve

Question 9

What is the major sites for biotransformation?

Answer 9

liver

- but also kidney proximal tubules, lungs, intestines, testes, skin epithelium, brain, plasma

Question 10

What role does Cytochrome P450 play in drug biotransformation?

Answer 10

if metabolized by CYP450 enzymes:

• inducers increase the enzyme levels (speeding up metabolism)
• inhibitors slow metabolism

Question 11

What is Vd?

Answer 11

volume of distribution = amount of drug in body / plasma concentration

NOTE: Vd is large when drug concentrates in a body compartment, thus it is better characterized as an apparent volume distribution

Question 12

What is induction? What is its role in drug-drug interactions?

Answer 12

inducers increase the enzyme levels (speeding up metabolism) -> quickly lowering plasma levels below minimal effective concentration

Question 13

What is inhibition? What is its role in drug-drug interactions?

Answer 13

inhibitors slow metabolism of any other drug metabolized by the same enzyme

Question 14

What is AUC?

Answer 14

area under the curve, sum of the area for each segment

Question 15

What is the total body water of a lean male?

Answer 15

60% body weight (kg)

Question 16

What is the total body water of a lean female?

Answer 16

55% body weight (kg)

Question 17

How do you calculate plasma volume (L)?

Answer 17

25% ECV

Question 18

How do you calculate ECV?

Answer 18

plasma volume + interstitial volume

Question 19

What is the difference between first-order and zero-order pharmacokinetics?

Answer 19

zero order kinetics: constant amount eliminated per unit

• drug elimination process is saturated
• amount of drug eliminated is independent of drug concentration

first order kinetics: constant fraction eliminated per unit of time

• drug elimination process is not saturated
• mass of drug eliminated is directly related to drug concentration
• • more typical form of drug elimination **