# Pharmacokinetics Flashcards Preview

## ► Med Misc 44 > Pharmacokinetics > Flashcards

Flashcards in Pharmacokinetics Deck (63)
1
Q

what is the thoeretical volume necessary to account for the total amount of drug in the body if it were present throughout the body in the same concentration as in the plasma

A

volume of distribution (Vd)

2
Q

can you measure Vd?

A

no its theoretical

3
Q

what is the shortened definition for Vd

A

theoretical volume measuring the amount of drug concentration you gave in the plasma

4
Q

what is the theoreical volume of plasma that is completly cleared (100% cleared) of drug in a given period of time, the units are in mL/min. Also can be defined as the bodies ability to eliminate a drug

A

Clearance (Cl)

5
Q

what is the time it take for the plasma concentration of a drug to fall by one-half

A

Elimination half time (T 1/2 Beta)

6
Q

what is the time it takes for the TOTAL AMOUNT OF THE DRUG in the body to decrease by one-half?

A

elinination half-life

7
Q

volume of Distribution: (Vd)

how do you calculate Vd?

A

by dividing the amount of drug injected by the plasma concentration

Vd = Q/C

8
Q

volume of Distribution: (Vd)

what is the Vd? do the math

A

Q=12

C= 2

Vd = Q/C

Vd = 12 / 2

Vd = 6 mL

9
Q

volume of Distribution: (Vd)

what is the voume of distribution

A

Q = 12

C = 1

Vd = Q / C

Vd = 12/1

Vd = 12 mL

10
Q

volume of Distribution: (Vd)

what is the Volume of distribution

A

Vd = Q /C

Vd = 12 / 3

Vd = 4mL

11
Q

volume of Distribution: (Vd)

which one has a LOW VD?

what type of drugs are these?

A

C

water loving drugs

Muscle relaxants (polar)

12
Q

volume of Distribution: (Vd)

which one has a large VD?

What drugs are these?

A

B

Induction agents (non-polar)

13
Q

what is Pharmacokinetics?

A

what the BODY does to the DRUG

14
Q

Body compartments:

The human body is schematically represented in the following figure. shown are the plasma volume (PV), interstitial Volume (ISV), intracellular volume (ICV), and fat adipose tissue.

A
15
Q

Body compartments:

what makes up the extra-cellular volume (ECV)

A

ISV and PV

ECV = ISV + PV

16
Q

Body compartments:

outline the ECV

A
17
Q

Body compartments: Distribution of drugs:

drugs with different properies have different volumes of distribution. MR, which are ionized are restricted to where?

A

extracellular space

18
Q

Body compartments: Distribution of drugs:

describe drugs that are confined to the ECV

ECV = ISV + PV

A

Muscle relaxants

Small Vd

Water Soluble

Ionized (polar-charged)

(bc they are water loving they are charged, charged molecules do not cross the lipid bylayers thus stay in the ECV and does not get into adipose tissue and have Small Vd)

19
Q

\Body compartments: Distribution of drugs:

what is the numerical value for SMALL Vd

A

0.3-0.5 L/kg

20
Q

Body compartments: Distribution of drugs:

what type of Vd does this picture depict

A

Large Vd

b/c the drug has moved into the ICV and adipose tissue

21
Q

Body compartments: Distribution of drugs:

describe drugs that have cause this

A

Induction agents

large Vd

Lipid Soluble

fat loving non-polar -uncharged

22
Q

Body compartments: Distribution of drugs:

what is the numerical value for a large Vd

A

2.0-2.5 L/kg

23
Q

Body compartments: Distribution of drugs:

on a weight basis the noenate/infant have an expanded ECV. see picture

A
24
Q

why do noenated need more SCh on a mg/kg basis? give 2 reasons

A
• greater Vd
• immature NMJ
• the NMJ is immature b/c they have inadequate number of nicotinic receptors, or the receptors may not be responsive to ACh.
• THE ECV of a neonate/infant is twice that of an adult.
25
Q

if neonate/infants need more SCh why do they need the same amount of NDMR as the adult on a weight base mg/kg basis?

A
• more NDMR is needed bc the ECV of the neonate is larger.
• Less drug is needed however b/c the NMJ is immature
• so less drug is needed to block the channels
• thus the cancel themselfs out and equal the same dose as an adult
26
Q

Kinetics:

what type is when a constant amount of the drug is eliminated per unit of time? ex 2 mp/min

A

Zero order kinetics

27
Q

Kinetics:

what does the graoh look like with zero order kinetics?

A

the concentration of the drug in the plasma falls linerally with time

28
Q

Kinetics:

what are the ONLY 3 drugs that are eliminated by zero order kinetics

A

ETOH

Phenytoin

ASA

29
Q

Kinetics:

is zero order an amount per unit of time or a fraction per unit time

A

an amount per unit time

30
Q

Kinetics:

Most drugs are eliminated how?

A

1st order kinetics

31
Q

Kinetics:

define 1st order kinetics

A

a constant fraction of a drug is eliminated per unit of time

32
Q

Kinetics:

drugs that are eliminated by 1st order behave in one of which 2 ways?

A

1 compartment

or

2 compartments

33
Q

Kinetics:

how can you always tell 1st order graph

A

it will have a log (ln) on the Y axis

34
Q

Kinetics:

what does the graph with 1st order 1 compartment model look like

A

like zero order but with a Log on the Y axis

35
Q

Kinetics:

what is the only drug that is eliminaed by 1st order kinetics 1 compartment model?

A

Albumin

36
Q

Kinetics:

what does the graph look like for 1st order 2 compartment elimination

A

a fast curvilinear line

37
Q

Kinetics:

name the drugs that are eliminated by 1st order 2 compartment model

A

all other drugs besides the zero order (ASA, ETOH, and Phenytoin) and the 1st order 1 compartment drug (albumin)

38
Q

Kinetics: 1st order 2 compartment

when in the graph is the Alpha phase and what does it represent?

A

distibution phase

39
Q

Kinetics:​ 1st order 2 compartment

where is the beta phase and what dose it represent?

A

elimination phase

40
Q

Kinetics:​ 1st order 2 compartment

where is the point of equilibrium?

A
41
Q

Kinetics:​ problem

what kind of plot is this? and how do you know?

A

1st order, 2 compartment

• it’s curved
• its a log (Y axis goes from 10 - 1,000)
42
Q

side note

when doing Vd i said the formula was

Vd= Q/C

flip to see real formula

A

Vd = Q / Cp (t=0)

you never have to worry obout the t=0 b/c we always assume it is just that 0 so i shortened it

43
Q

Kinetics:​ problem​

label the distribution part and the elimiantaion part

as well as the alpha and beta

A
44
Q

Kinetics:​ problem​

find the concentration of the drug at t = 0 if the drug is distributed instantaneously into its volume of distribution (and describe how you found it)

A

find the equilibrium point and follow angle of the beta slope

100 mg/L

45
Q

Kinetics:​ problem​

2500 mg of a drug was administered and plotted on the graph. what is the Vd if this drug

A

Vd = Q / Cp (t=0)

Q= 2500 mg

Cp (t=o) = 100 mg/L

Vd = 2500 / 100

Vd = 25 L

46
Q

Kinetics:​ problem​

what is the T 1/2(beta) of this drug?

or the half-time elimination

A

find the concentration at equilibrium time 0. (100)

then find 1/2 that (50)

see where it meets the graph on the beta axis

47
Q

Kinetics:​ problem​

2 mg of a drug is given what is the Vd?

A

watch the trick plasma concentration is in mcg and the drug is in mg- convert one to the other

Cp(t=o) = 100mcg/L

Q = 2mg or 2000mcg

2000/100 = 20 L

Vd = 20 L

48
Q

half life problems:

a drug is eliminated by 1st order kinetics and has a 1/2 life of 6 hours how much drug remains after 18 hours if 10 mg is administered

A

1.25 mg

49
Q

half life problems:

160 mg of a drug is administed and 20 mg remain 30 hours later. how much of the is lost in the next 20 hours, if the drug is eliminated by first ordr kinetics

A

15 mg more will be lost

50
Q

half life:

how may 1/2 lives (1/2 times) are required to eliminate 98% of a drug

A

6

51
Q

Pharmacokinetics: Hepatic metabolism

how many phases of reactions are there?>

A

3

52
Q

Pharmacokinetics: Hepatic metabolism

what phase is when the reactions involving chemical biotransformation of a molecule, usually to more water soluble and often inactive metabolites

A

Phase I

53
Q

Pharmacokinetics: Hepatic metabolism

what are the 4 types of phase I reactions

A

oxidation

reduction

methylation

hydrolysis

54
Q

Pharmacokinetics: Hepatic metabolism

what enzyme is responsible for many of the phase I reactions (oxidation, reduction, methylation, hydrolysis).

A

cytochrome P-450 system

55
Q

Pharmacokinetics: Hepatic metabolism

what phase reaction invlove conjugation of a drug or its metabolite w/ endogenous molecules; conjugation reactions make drugs water soluble for excretion by the kidneys or billary system.

A

Phase II

56
Q

Pharmacokinetics: Hepatic metabolism

what are types of Phase II reactions

A

glucuronidation, gluthathione conjugation, sulfation and ACETYLATION

57
Q

Pharmacokinetics: Hepatic metabolism

what phase reaction are eliminatin reactions that involve ATP-binding cassette (ABC) transport proteins?

A

Phase III

58
Q

Pharmacokinetics: Hepatic metabolism

Quickly describe each Phase reaction

A
• Phase I- oxidation, reduction, methylation, hydrolysis
• Phase II- Acetylation
• Phase III- ATP-binding cassette (ABC)
59
Q

Pharmacokinetics: protein binding

most drugs bind to what?

A

plasma proteins

60
Q

Pharmacokinetics: protein binding

what is the most abundant plasma protein

A

Albumin

61
Q

Pharmacokinetics: protein binding

do protein bound drugs leave circulation

A

no- only free unbound drugs do

62
Q

Pharmacokinetics: protein binding

patients who have ______ are more sensitive to injected drugs b/c protein binding is reduced. thus more of the drug is free or unbound

A

Hypoproteinuria (hypoalbuminemia)

63
Q

Pharmacokinetics: protein binding

when protein binding is decreased what happens to Vd?

A

it is increased