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Pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What are the basic processes of pharmacokinetics?

A

ADME

Absorption, Distribution, Metabolism, Excretion

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2
Q

What is the difference between pharmacokinetics and pharmacodynamics?

A

Kinetics: effects of body on drug
Dynamics: how drugs affect body

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3
Q

What factors affect absorption?

A

Rate of dissolution (how long to break down)

Surface area

Blood flow

Lipid solubility (how quickly cross membrane)

pH partitioning (ion trapping)

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4
Q

What route is suitable for large volumes and easily adjusted?

A

IV (bypass absorption barriers)

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5
Q

Which routes are suitable for oily substances and suspensions?

A

IM

SQ

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6
Q

Most common transport mechanism for drugs

A

simple diffusion

~non-protein

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7
Q

3 ways drugs and cross cell membrane

A

facilitated diffusion (rare)

active transport

direct penetration= simple diffusion (most common)

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8
Q

What transport system kicks drugs out of cells?

A

P-glycoprotein

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9
Q

Which type of drugs can easily cross the cell membrane?

A

nonpolar drugs

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10
Q

Which drugs can’t dissolve in or cross cell membranes easily?

A

polar drugs

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11
Q

In what form can weak acids and bases cross membranes?

A

only in unionized form

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12
Q

Lower pH, more likely…

A

molecule has H+ attached

–>ion trapping

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13
Q

Where is a weak base trapped?

A

acidic compartments–> so many H in solution, it can’t ditch one to become ionized

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14
Q

Where is a weak acid trapped?

A

basic compartments–> can’t find H to stabilize since not enough in solution

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15
Q

Where are weak acids absorbed readily?

A

acidic–> stomach

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16
Q

Are weak acids readily absorbed in the stomach?

A

No since stomach is acidic

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17
Q

What body fluids can ion-trap drugs?

A 
Urine
Breast milk
Jejunum, ileum
Stomach
Prostate
Vagina
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18
Q

What is Ka?

A

rate constant for absorption

per unit time

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19
Q

What is S?

A

Salt factor

drugs often given as their salt

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20
Q

What is the S value?

A

less than 1

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21
Q

What is F?

A

bioavailability

= amount of drug that reaches bloodstream

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22
Q

What is the value of F?

A

less than 1

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23
Q

What is the equation to find bioavailability (F)?

A

Area under curve of route used/ AUC IV

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24
Q

How to configure amount of drug absorbed

A

S * F * Dose

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25
Q

What is volume distribution (Vd)

A

amount of drug in body divided by plasma concentration

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26
Q

What happens to Vd when there is a lot of drug in the body

A

gets very large although there is very little in the plasma

know how much you gave, not in the plasma so must be elsewhere in the body

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27
Q

What is Cp?

A

concentration of drug in plasma

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28
Q

How to calculate Cp for 1 compartment model

A

S * F * Dose / Vd

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29
Q

What comprises extracellular volume?

A

plasma and interstitial

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30
Q

What comprises total body water?

A

extracellular + intracellular volumes

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31
Q

TBW of lean male

A

60% body weight (kg)

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32
Q

TBW of lean female

A

55% body weight (kg)

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33
Q

How to calculate extracellular volume

A

1/3 TBW

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34
Q

How to calculate plasma volume

A

25% of extracellular volume

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35
Q

How to calculate Cp for 2 compartment model

A

Once distributed, calculate t 1/2 for elimination

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36
Q

Site of peripheral drug concentration

A

Fat
Tissue
Bone
Transcellular reservoir (stomach)

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37
Q

What peripheral site stores lipid-soluble drugs

A

fat

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38
Q

Where do tetracycline abx accumulate

A

bone

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39
Q

How is stomach a transcellular reservoir

A

stores drugs that are slowly absorbed or undergoing enterohepatic circulation

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40
Q

When is Vd larger than TBW?

A

drug concentrates in a body compartment instead of plamsa–> apparent Vd

tetracycline, etc.

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41
Q

When is Vd lowest?

A

when in plasma

plasma< extracellular< intracellular < TBW < peripheral site

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42
Q

What affects drug distribution

A

ability of drugs to enter cells (same as absorption)

blood flow to tissues

ability of drugs to exit vasculature (lipid easier)

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43
Q

When is a drug bioactive?

A

when free in blood (alpha)

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44
Q

Why is alpha (drug bioactivity) important?

A

potential toxicity

new drugs displace bound and cause more drug to be free

–> if drug 90% bound, new drug added and now 80% bound, alpha doubled (eventually eliminated but double concentration for a period of time)

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45
Q

What is the blood brain barrier a barrier against?

A

ionized or polar drugs UNLESS they have a transporter

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46
Q

Where is the primary site of biotransformation (metabolism)

A

liver

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47
Q

What is the function of liver in regards to metabolism in ADME

A

primarily inactivates drug, but can activate pro-drugs

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48
Q

Why is the liver so important in terms of excretion?

A

lipophilic drugs must be made polar so they can be trapped in the renal tubular fluid

49
Q

What are secondary areas of metabolism of drugs?

A 
kidney
lungs
intestines
testes (Sertoli)
skin epithelia
brain 
plasma
50
Q

Stages of Phase 1 Metabolism

A

oxidation
reduction
hydrolysis

51
Q

What is the purpose of phase 1 of drug metabolism?

A

make polar metabolites

add or unmask group

52
Q

What enzymes are vital to phase 1 of metabolism and where are they located?

A

Cytochrome P450 in SER

–>oxidative process

53
Q

What do inducers of CYP450 do?

A

increase enzyme levels–> speed up metabolism so lower total plasma levels below MEC

54
Q

Examples of CYP450 inducers

A

phenobarbital
carbamazepine
ethanol
cigarette smoke

55
Q

What do CYP450 inhibitors do?

A

inhibit enzyme–>slow metabolism–> toxic levels

56
Q

Examples of CYP450 inhibitors

A

erythromycin
ketoconazole
metronidazole
grapefruit juice

57
Q

What specific CYP450 enzyme does grapefruit juice inhibit?

A

CYP3A4

58
Q

What is the mechanism of grapefruit juice in metabolism?

A

inhibits CYP3A4 in intestinal epithelial cells

increase BIOAVAILABILITY of other drugs so more enter blood

59
Q

What 3 processes can occur in phase 2 of biotransformation?

A

conjugation
acetylation
methylation

60
Q

What is the function of acetylation and methylation in metabolism?

A

make drug LESS water soluble–> REDUCE drug activity

AKA inactivates drug

61
Q

What is the major route of metabolism for drugs and endogenous compounds that occurs in the ER?

A

Glucuronidation

62
Q

What is another major route of drug metabolism that occurs in the cytoplasm?

A

sulfation

63
Q

What is the function of conjugation in phase 2 metabolism?

A

add highly POLAR molecule to make drug MORE water soluble and more excretable

64
Q

What is the difference between conjugation and acetylation/methylation?

A

conjugation adds polar group to make MORE water soluble

acetylation/methylation makes drug LESS water soluble to inactivate it

65
Q

Which aspect of conjugation is inducible?

A

glucuronidation

66
Q

Why does first-pass metabolism decrease bioavailability of oral drugs?

A

since the drug goes to the GI tract then the liver, small amount of drug is transferred to blood

–>why IV used if need more or fast drug

67
Q

What is the major route of drug elimination?

A

Kidney

68
Q

What are minor routes of drug elimination?

A

bile
sweat
breath
breast milk

69
Q

What are the steps in drug elimination?

A

Glomerular filtration

Passive tubular reabsorption

Active tubular secretion

70
Q

What drugs don’t filter in the glomeruli?

A

protein-bound drugs

71
Q

What drugs are reabsorbed passively in tubular reabsorption during elimination?

A

lipid soluble drugs

unionized weak acids and bases

72
Q

How do we eliminate protein-bound drugs?

A

active tubular secretion

–>when drug temporarily displaced from protein binding sites near proximal tubule

73
Q

What modify renal drug excretion?

A

pH-dependent ionization (affects passive)

competition for active tubular transport

age (GFR decreases)

74
Q

What is the excretion rate?

A

mass eliminated per unit time

75
Q

Excretion rate _____ as plasma concentration increases

A

increases

76
Q

What is clearance?

A

plasma volume of solute removed per time

FLOW RATE

77
Q

Clearance _____ as plasma concentration change

A

remains constant

78
Q

If clearance decreases by half, solute_____

A

doubles

79
Q

eGFR

A

(140-age) x BW / 72 * serum creatinine

80
Q

What to do to eGFR equation if female

A

multiply by .85

81
Q

What is special about allergy or hypersensitivity drug effect?

A

not dose related

requires prior sensitization

82
Q

What are the most serious drug allergies to?

A

penicillin family most serious

sulfa drugs common

83
Q

Lack of plasma esterase and succinylcholine

A

apnea of long duration

84
Q

Lack of NADH methemoglobin reductase and nitrites, sulfonamides, primaquine

A

hereditary methemoglobinemia

85
Q

low liver acetyl transferase and isoniazid (treats TB)

A

increased toxicity

86
Q

lack of G6P dehydrogenase (low GSH) and primaquine

A

drug-induced hemolytic anemia (favism)

87
Q

Deficiency of porphobilinogen deaminase and barbiturates, estrogens, sulfonamides, chloroquine

A

acute intermittent porphyria

88
Q

Hepatotoxic drugs

A 
lipid-lowering
antiseizure
TB
antiretroviral
oral hypoglycemics
antifungal
immunosuppressants
acetaminohpen
89
Q

Terfenadine (seldane) caused

A

QT prolongaiton, torsades de pointes–>drop dead

90
Q

What drugs have greatest carcinogenic potential

A

cancer chemotherapeutic drugs
–> diethylstilbestrol (DES)
used to prevent miscarriage, caused uterine and vaginal cancer in daughters

91
Q

Neonate and infants have __________ TBW c/t adults

A

increased

92
Q

metabolism of drugs is ___ in children

A

faster but similar ADE

93
Q

Describe ADME in infants

A

A increased or decreased
D: low albumin so higher protein bound drugs, BBB not developed so drugs can cross
M: decreased (adjust downward)
E: decreased (adjust downward)

94
Q

What fraction of patients respond to placebo

A

1/3

95
Q

What percent of patients respond to placebo when used for pain

A

75%

96
Q

Describe drug therapy physiologic changes during pregnancy

A

decreased bowel tone and motility–> increased time for drug absorption

increased hepatic metabolism

increased GFR

97
Q

Which kinetics describes amount of drug eliminated is independent of drug concentration

A

zero order

98
Q

Which kinetics is constant amount eliminated per unit with drug elimination saturated

A

zero

99
Q

equation for zero order kinetics

A

change in plasma concentration over change in time= constant (k)

100
Q

Example of zero order drug

A

ethanol

101
Q

Which kinetics is constant fraction eliminated per unit time

A

first order

102
Q

Which kinetics is not saturated, where mass of drug eliminated is DIRECTLY related to the concentration

A

first order

103
Q

Equation for first order kinetics

A

change in plasma concentration over change in time= constant (k) multiplied by plasma concentration

104
Q

Which kinetics is the more typical form of drug elimination

A

first order

105
Q

In first order kinetics, each subsequent half-life_____ the concentration

A

halves

1= 50%
2= 25%
3= 12.5%
106
Q

97% drug eliminated in ____ half-lives

A

5

107
Q

first order kinetics calculation

A

0.693= k*t1/2

108
Q

what is tau

A

dosage interval

qd-> 24 tau

109
Q

CPss (ave)

A

plasma concentration at steady-state plateau where input=output

110
Q

clearance equation

A

clearance= Kel (first order elimination rate constant) * Vd

OR

S * F * (dose/tau)/ Cp

111
Q

When do you see hockey stick kinetics graph

A

drugs at high concentrations

starts out as 0–> 1

112
Q

Rate of elimination equation

A

Vmax * Cp/ Km + Cp

113
Q

Steady-state concentrations proportional to…

A

dose/dosage interval OR F/Cl

114
Q

Cpss (ave) =

A

dosing rate/ clerance

1.44 * S * F * D * t 1/2 / tau * Vd

115
Q

loading dose equation

A

Cpss (ave) * Vd / (S * F)

116
Q

Plasma concentration with varying dosages

A

have proportional changes in peak concentration

117
Q

Plasma concentration with varying absorption rates

A

more rapid absorption give higher peak (line goes below average as times goes on)

if 1/3, goes above with time

118
Q

Plasma concentration with varying elimination rates

A

higher peak with slower elimination, line above average

Pharmacology (6 decks)

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