lecture 3 - absorption and half-life

Question 1

describe the extent of absorption

Answer 1

reflects the total amount of the drug entering the body. Is not dependent on time.
bioavailability

Question 2

describe the rate of absorption

Answer 2

determines how quickly the drug enters the body. The rate typically changes with time

Question 3

physiological determinants of extend

Answer 3

fraction absorbed

• physiochemical properties of a drug
• properties of the gut wall
  (e. g metabolic enzymes, transporters)

first pass extraction (ER)

• metabolisms of drug by liver
  (e. g. hepatic BF, enzyme numbers)

Question 4

physiological determinants of the rate of drug absorption

Answer 4

bolus input
- rapid absorption rate, IV injection

zero-order
- constant absorption rate, IV

first-order
- absorption rate proportional to the amount of drug at administration site, intramuscular injection

Question 5

describe half-life

Answer 5

describe first-order processes

commonly used in pharmacokinectics to describe drug absorption and elimination

elimination half-life determines how quickly a drug accumulates. Determined by CL and V

Question 6

describe accumulation factor

Answer 6

is the ratio of the concentration at steady state to the concentration after the first dose at the same time after the dose
if the dosing interval is equal to the half-life then the accumulation factor is exactly 2

Question 7

what does the extent of accumulation depend on

Answer 7

the dosing interval and the half-life

Question 8

after one half-life…

Answer 8

50% of drug has been accumulated

50% of drug has been eliminated

Question 9

after 2 half-lives…

Answer 9

75% of drug has been accumulated

75% of drug has been eliminated

Question 10

after 4 half-lives…

Answer 10

steady state is considered to have been reached