Lecture 3 - pharmacokinetic modelling Flashcards Preview

Pharma midterm 1 > Lecture 3 - pharmacokinetic modelling > Flashcards

Flashcards in Lecture 3 - pharmacokinetic modelling Deck (29)
Loading flashcards...
1
Q

What do pharmacokinetic models describe?

A

They are relatively simple mathematical schemes that represent complex physiological spces or processes

2
Q

What are the most commonly used pharmacokinetic models?

A

comparatmental models

3
Q

Why do we measure the plasma drug conecntration?

A

it provides us with useful information about how much drug is in the tissue, beacuse it is generally related to the plasma concentration

4
Q

What do we measure with the zero-order elimination model?

A

the plot of the log of the plasma concentration vs time, constant amount of drug is eliminated per unit time

5
Q

When can there be zero-order elimination?

A

when therapeutic doses of drugs exceed the capacity of elimination mechanisms

6
Q

What is first-order elimination?

A

it refers to the elimination of a constant fraction of drug per unit time

the rate of elimination is a linear function of the plasma drug concentration

7
Q

When does first order elimination occur?

A

when elimination systems are not saturated by the drugs

a constant fraction of drug is eliminated per unit ti,,e

8
Q

What is a one-compartment open model?

A

when the body is seen as one continous fluid phase into which the drug is administered and through which it diffuses

9
Q

What is meant by open model

A

open= continous loss of drugs from the compartment due to metabolism end excretion

the openness of the body causes drug molecules to disengage from receptors and so terminates drug action

10
Q

What formula can describe the drug concentration following a single IV administration

A
11
Q

What is elimination half life?

A

the time it takes for the plasma drug concentration to be reduced by 50%

12
Q

What drugs does the half life concept apply to?

A

only drugs that aare eliminated by first order kinetics

13
Q

how is half-life determined?

A

log plasma drug concentration

vs

time profile for drugs fitting a one-compartment model

or from the elimination phase for drugs fitting the two-compartment model

14
Q

what is the general rule for all doses in which first-order elimination occurs, in regards to half-life?

A

>95% of the drug will be eliminated in a time interval equal to five half-lives

15
Q

What is C0

A

plasma concentratio at 0 time

16
Q

Cmax?

A

peak plasma concentration following a single non-iv dose of drug

17
Q

Tmax

A

time of peak plasma concnetration

18
Q

T1/2el

A

half life of elimination

19
Q

AUC

A

area under the curve

under the plot of concentration of drug in plasma against time

represents the total amount of drug absorbed by the body, irrespective of the rate of absorption

20
Q

What is the two-compartment model used for?

A

distribution and elimination of drugs

21
Q

How does a two-compartmend model work?

A

initial rapid changes in the plasma concentration of a drug are observed beacuase of distribution phase, the time required for the drug to reach an equilibrium distribution between a central compartment, plasma space, and a second compartment such as aggregate tissues and fluids to which the drug distributes

22
Q

what is meant by two compartments being notational?

A

they do not bear a constant relationship to the familiar physiological compartments

23
Q

Characteristics of the central compartment?

A

allows rapid, more or less instantaenous equilibrium

blood, interstitial fluid and highly perfused organs - heart, liver, lungs and kidney

24
Q

what is the peripheral compartment

A

comes to equilibrium woth the central compartment more slowly

less well perfused organs - skin, bone, fat

25
Q

what is the noncompartmental PK analysis dependent upon?

A

estimation of total drug exposure

26
Q

How is total drug expose estiamted?

A

by the area under the curve methods, trapezoidal rule

27
Q

What is the trapezoidal rule?

A

divide the plasma concentration-time profile to several trapezoids and add the AUC of these trapezoids

28
Q

How is the concentration-time or curve described?

A

in term of sloped

heights

areas

moments

SHAM

29
Q

What can we calculate with the SHAM values?

A

respective disposition half lived

and

Vd area