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Basic Pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

what is the goal of drug therapy?

A

deliver and maintain therapeutic, yet non-toxic, concentration of the most appropriate drug in the target tissue and achieve the therapeutic objective without adversely affecting the patient

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2
Q

what is a dose?

A

a specific amount of a drug taken at one time

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3
Q

what is a dosage?

A

an amount- mg/kg- at a specific interval for a specified amount of time, by a given route

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4
Q

what is the difference between topical and transdermal application of a drug?

A

topical is not supposed to go systemic- not systemic concentrations
transdermal is supposed to have an impact systemically

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5
Q

why is formulation important?

A

the specific formulation or salt of an active ingredient can markedly change its characteristics
ceftiofur has different formulations for different species/different routes of injection

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6
Q

what does formulation change?

A

pharmacokinetic properties
not pharmacodynamic properties

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7
Q

what route of administration is the most accurate dosing?

A

intravenous

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8
Q

what happens in intramuscular or subcutaneous administration?

A

must be absorbed into systemic circulation
cannot be irritating formulation

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9
Q

what is the safest route of administration?

A

oral
also most variable

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10
Q

true/false: overall drug exposure can be a lot lower in oral administration

A

yes
not all gets into blood stream

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11
Q

what is the major site of absorption of oral drugs?

A

duodenum

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12
Q

what are the sources of variability for oral drugs?

A

species
diet
food consumption
GI disease

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13
Q

what should you think about with topical medications?

A

goal is to have drug stay at site of application
high local concentrations
safer, but can get local reactions and might go systemic

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14
Q

what is pharmacokinetics?

A

disposition of drugs in the body
description of movement of a drug over time through the body

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15
Q

what is the underlying assumption of pharmacokinetics?

A

a relationship exists between the pharmacological or toxic response to a drug/chemical and the concentration of the drug in an easily measurable compartment

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16
Q

what is the shape of the drug clearance in IV administration of a drug?

A

exponential

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17
Q

does IM always have the highest peak in the time-concentration curve?

A

not always- depends on drug

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18
Q

what does the area under the time-concentration curve reflect?

A

how much drug is in circulation and how long it stays there

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19
Q

at ______________________, the amount of drug we are giving is equal to the amount of drug the body is eliminating per unit time

A

steady state

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20
Q

what are the physiologic processes of a drug in the body?

A

absorption
distribution
metabolism
excretion

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21
Q

what are the physical factors of the drug that affect absorption?

A

solubility: GI or at site of injection
chemical stability
feed
formulation
ability to cross membranes

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22
Q

what are the modifying factors of absorption?

A

contact time
surface area
blood flow to site of absorption

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23
Q

from plumb’s drug handbook: “oral systemic antibiotics should not be administered in patients with septicemia, shock, or other grave illnesses, as absorption of the drug from the GI tract may be delayed or diminished.” why does it say this?

A

blood flow to the intestines may be decreased

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24
Q

how does the solubility of drugs affect their distribution?

A

stay in systemic or interstitial fluid if water soluble
enter cells or go into fat or lipid environments if sufficiently lipid soluble

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25
Q

what are important factors in distribution of a drug?

A

binding to plasma or red cell proteins
ability to cross membranes
blood flow to tissues
tissue solubility or binding of the drug

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26
Q

what can the ability to cross membrane barriers influence?

A

how much is absorbed
rate of absorption
access to certain body spaces
whether a drug can be found intracellularly

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27
Q

what are the primary blood proteins that can bind to drugs?

A

albumin
lipoproteins
alpha 1-acid glycoprotein

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28
Q

what is the most important way for drugs to cross barriers?

A

passive diffusion

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29
Q

what determines lipophilicity?

A

size
presence of polar groups
ionization

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30
Q

an acid is non-ionized in ________________________; a base is non-ionized in _________________________

A

acid environment
basic environment

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31
Q

what is ion trapping?

A

a drug will be “trapped” at a higher concentration were it is most ionized

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32
Q

what are the active transport mechanisms for a drug crossing a membrane?

A

carrier-mediated active transport
transport pumps

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33
Q

what active transport mechanism for a drug crossing a membrane follows the concentration gradient and which one goes against it?

A

carrier-mediated follows the gradient
transport pumps pump against it

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34
Q

where are transport pumps found?

A

normal membranes: intestinal wall, blood-brain barrier, renal tubules, placental membranes
cancer cells
bacteria

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35
Q

what is P-glycoprotein and where is it found?

A

a transport protein
intestinal epithelium
blood-brain barrier
renal tubules

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36
Q

what makes up the blood-brain barrier and how does this affect drugs?

A

tight junctions
no intracellular pores or pinocytotic vesicles
active efflux transport proteins
highly lipophilic drugs tend to enter central nervous system
compromised during inflammation

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37
Q

true/false: water-soluble drugs tend to have a wider distribution

A

false: lipid soluble drugs do because they cross membranes more readily

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38
Q

what is the main objective of enzymatic biotransformation?

A

convert lipid-soluble drugs into more polar, less lipid soluble metabolites that are more easily excreted

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39
Q

what are the pharmacodynamic consequences of drug metabolism?

A

loss of pharmacological activity
maintenance of activity through pharmacologically active metabolites
formation of pharmacologically active compound from non-active prodrug
formation of toxic metabolites

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40
Q

what is the major site of biotransformation?

A

liver

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41
Q

what catalyzes the majority of Phase I reactions?

A

cytochrome P450 system

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42
Q

what happens in phase I or functionalization reactions?

A

parent drug is converted to a more polar metabolites through oxidation, reduction, or hydrolysis

43
Q

what does insertion of oxygen by cytochrome P450 do?

A

creates wide variety metabolic transformations and polar metabolites

44
Q

what are the clinical implications of cytochrome P450?

A

drug interactions: inhibition (decreased elimination) vs induction (increased elimination)
liver disease
genetic variation in P450 levels
infectious disease can affect activity

45
Q

what is one group of dogs with lower drug metabolizing capacity?

A

sight hounds

46
Q

what are phase II or conjugation reactions responsible for?

A

increasing water-solubility of a product by conjugation with endogenous substrates

47
Q

what is one important thing phase II reactions do with detoxifying phase I metabolites?

A

glutathione conjugation

48
Q

what are the types of conjugation reactions undergone in phase II?

A

glucuronidation
sulfate conjugation
acetylation
glutathione conjugation
methylation

49
Q

what species is deficient in glucuronidation of some drugs?

A

cats

50
Q

what species do no acetylate or are low?

A

dogs do not acetylate
cats are low

51
Q

why is glutathione conjugation important?

A

very important in protecting agains reactive toxic metabolites

52
Q

how do you calculate the rate of renal excretion?

A

filtration+secretion-reabsorption

53
Q

what can pass through glomerular filtration?

A

free drugs
non-protein drugs- limited by size of pores

54
Q

true/false: monoclonal antibodies are likely to be cleared by glomerular filtration

A

false: proteins will not

55
Q

what is secreted by tubular secretion?

A

acidic and basic substances
can be very efficient

56
Q

what method of reabsorption is most important in tubular reabsorption?

A

passive
pH can affect because only unionized drugs are reabsorbed

57
Q

what is enteral?

A

via the gastrointestinal tract

58
Q

what is parenteral?

A

routes other than enteral

59
Q

what is the first pass effect?

A

the loss of drug degraded during its first passage through the liver and intestinal wall after absorption from the GI tract

60
Q

what is enterohepatic recirculation?

A

process by which drug metabolites are excreted in bile, then the parent drug is reabsorbed from the gut

61
Q

how does enterohepatic recirculation affect a drug in the body?

A

increases absorption phase
greater exposure of intestine to drugs
can create a series of plasma peaks as the drug recirculates
can increase overall bioavailability

62
Q

what is the systemic dose equation?

A

the oral dose administered multiplied by the bioavailability (F)

63
Q

how do you calculate bioavailability?

A

bioavailability (F) of oral= Area under the curve of oral divided by the area under the curve of IV

64
Q

what should you think about with bioavailability?

A

greatest impact when bioavailability is low
if do rectal administration, 50% of circulation from rectal region bypasses the liver
first pass effect can be a site of drug interactions

65
Q

Maropitant (Cerenia) is dosed at 1mg/kg SC, IV or 2-8mg/kg PO. given this information alone, what would you predict its bioavailability is?

A

much less than 100%, maybe 50% or less

66
Q

why are mathematical pharmacokinetics helpful?

A

allows us to describe what happens
predicts time to onset, magnitude, and duration of effect
helps us design drug dosage regimens
helps us to predict the magnitude of a change in drug concentrations in a patient

67
Q

the decrease in drug concentration is exponential-____________________________________________

A

a fixed fraction is lost with each unit of time

68
Q

what does the distribution phase of the drug plasma concentration over time graph show?

A

the time where the drug is distributed to the tissues- an initial steep decline in concentration

69
Q

what is half-life?

A

time it takes for drug concentration to drop 50%, or time it takes for half of the drug to be eliminated from the body
t1/2

70
Q

in five half-lives, over ____ of the drug is eliminated

A

95%

71
Q

in ten half-lives, over ____ of the drug is eliminated

A

99.9%
reference point for contamination of food products

72
Q

what is apparent volume of distribution (Vd)?

A

the conceptual volume in which the drug would have to be dissolved to achieve the concentration (Co) observed in the plasma
relates the total amount of a drug in the body to the plasma concentration of that drug

73
Q

what are the equations for calculating Vd and Co?

A

Vd=dose/Co=mg/kg/mg/ml=ml/kg
Co=dose/Vd
dose=Co x Vd

74
Q

how do you calculate plasma concentration of a drug?

A

amount of drug in body divided by volume of distribution (ml)
dose of drug (mg/kg) divided by volume of distribution (ml/kg)

75
Q

does Vd indicate penetration into specific sites?

A

no

76
Q

what is clearance (Cl)?

A

conceptual: volume of plasma or blood that would have to be completely cleared of drug to account for its removal per unit of time
a proportionality constant that reflects the rate at which drug is cleared from the plasma

77
Q

what makes up drug clearance?

A

hepatic clearance+renal clearance+other routes

78
Q

what makes up drug elimination?

A

drug metabolism and drug excretion

79
Q

at steady state, ________________ and __________________ are equal

A

rate of elimination and dosing rate

80
Q

what is dosing rate?

A

dose of drug per unit time

81
Q

what is the equation for clearance at a steady state?

A

rate of elimination/Css
Css=average steady state drug concentration

82
Q

what is the equation for clearance after a single injection?

A

Cl=dose/AUC
AUC= area under the curve

83
Q

clearance is _____________ of concentration of drug in the blood

A

independent

84
Q

what is drug elimination?

A

amount of drug cleared from the blood per unit time
Cl x drug concentration

85
Q

clearance predicts the __________________________________________ in multiple dosing

A

average steady state plasma concentration

86
Q

what is zero order kinetics?

A

drug elimination processes become saturated and a fixed amount is cleared per unit time
can lead to overdose/more toxic effects

87
Q

what is the slope of the drug concentration over time?

A

-k or Kel

88
Q

what is the equation for half-life using the slope of the concentration over time graph

A

t1/2=0.693/Kel
=0.693(Vd/Cl)

89
Q

what are the primary parameters of pharmacokinetics?

A

volume of distribution and clearance
half-life is the most useful secondary parameter

90
Q

half-life is ________________ on Cl and Vd, but Cl and Vd are ________________

A

dependent
independent

91
Q

how long does it take to achieve steady state?

A

five half-lives
time is independent of dosage

92
Q

when will drug accumulation occur?

A

when dosing interval is less than 2 half-lives
the shorter the interval, the more significant the accumulation

93
Q

if the dosing interval is greater than ______________, accumulation of the drug is negligible

A

3-5 half-lives

94
Q

why would we give a loading dose?

A

to reach therapeutic concentrations more quickly
may still take 5 half-lives to reach stable steady state concentrations

95
Q

what is the equation for loading dose?

A

loading dose= Vd x desired concentration

96
Q

duration of drug action is extended by ______________ when the dose is doubled

A

one half-life

97
Q

what does it mean for two drugs to interact with inhibition?

A

decreased elimination- toxicity

98
Q

what does it mean for two drugs to interact with induction?

A

increased elimination- loss of therapeutic effect

99
Q

when you change the formulation of a drug, does pharmacodynamics or pharmacokinetics or both change?

A

pharmacokinetics changes
pharmacodynamics does not

100
Q

what would impact blood flow to the site of absorption?

A

sick animals may have reduced blood flow to intestine and decreased absorption
dehydrated animals/low blood pressure might have reduced subcutaneous and intestinal blood flow

101
Q

how prominent are changes in protein binding?

A

clinically significant effects relatively rare

102
Q

what drugs interact with cytochrome P450?

A

Phenobarbital: induces
Ketoconazole: inhibits

103
Q

what is the first pass effect?

A

loss of drug degraded during its first passage through the liver after absorption from the GI tract

104
Q

what is enterohepatic recirculation?

A

process whereby drug metabolites are excreted in the bile amd then the parent drug is re-absorbed from the gut

Basic Pharmacology (37 decks)

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