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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
what are important factors in distribution of a drug?
binding to plasma or red cell proteins ability to cross membranes blood flow to tissues tissue solubility or binding of the drug
26
what can the ability to cross membrane barriers influence?
how much is absorbed rate of absorption access to certain body spaces whether a drug can be found intracellularly
27
what are the primary blood proteins that can bind to drugs?
albumin lipoproteins alpha 1-acid glycoprotein
28
what is the most important way for drugs to cross barriers?
passive diffusion
29
what determines lipophilicity?
size presence of polar groups ionization
30
an acid is non-ionized in ________________________; a base is non-ionized in _________________________
acid environment basic environment
31
what is ion trapping?
a drug will be "trapped" at a higher concentration were it is most ionized
32
what are the active transport mechanisms for a drug crossing a membrane?
carrier-mediated active transport transport pumps
33
what active transport mechanism for a drug crossing a membrane follows the concentration gradient and which one goes against it?
carrier-mediated follows the gradient transport pumps pump against it
34
where are transport pumps found?
normal membranes: intestinal wall, blood-brain barrier, renal tubules, placental membranes cancer cells bacteria
35
what is P-glycoprotein and where is it found?
a transport protein intestinal epithelium blood-brain barrier renal tubules
36
what makes up the blood-brain barrier and how does this affect drugs?
tight junctions no intracellular pores or pinocytotic vesicles active efflux transport proteins highly lipophilic drugs tend to enter central nervous system compromised during inflammation
37
true/false: water-soluble drugs tend to have a wider distribution
false: lipid soluble drugs do because they cross membranes more readily
38
what is the main objective of enzymatic biotransformation?
convert lipid-soluble drugs into more polar, less lipid soluble metabolites that are more easily excreted
39
what are the pharmacodynamic consequences of drug metabolism?
loss of pharmacological activity maintenance of activity through pharmacologically active metabolites formation of pharmacologically active compound from non-active prodrug formation of toxic metabolites
40
what is the major site of biotransformation?
liver
41
what catalyzes the majority of Phase I reactions?
cytochrome P450 system
42
what happens in phase I or functionalization reactions?
parent drug is converted to a more polar metabolites through oxidation, reduction, or hydrolysis
43
what does insertion of oxygen by cytochrome P450 do?
creates wide variety metabolic transformations and polar metabolites
44
what are the clinical implications of cytochrome P450?
drug interactions: inhibition (decreased elimination) vs induction (increased elimination) liver disease genetic variation in P450 levels infectious disease can affect activity
45
what is one group of dogs with lower drug metabolizing capacity?
sight hounds
46
what are phase II or conjugation reactions responsible for?
increasing water-solubility of a product by conjugation with endogenous substrates
47
what is one important thing phase II reactions do with detoxifying phase I metabolites?
glutathione conjugation
48
what are the types of conjugation reactions undergone in phase II?
glucuronidation sulfate conjugation acetylation glutathione conjugation methylation
49
what species is deficient in glucuronidation of some drugs?
cats
50
what species do no acetylate or are low?
dogs do not acetylate cats are low
51
why is glutathione conjugation important?
very important in protecting agains reactive toxic metabolites
52
how do you calculate the rate of renal excretion?
filtration+secretion-reabsorption
53
what can pass through glomerular filtration?
free drugs non-protein drugs- limited by size of pores
54
true/false: monoclonal antibodies are likely to be cleared by glomerular filtration
false: proteins will not
55
what is secreted by tubular secretion?
acidic and basic substances can be very efficient
56
what method of reabsorption is most important in tubular reabsorption?
passive pH can affect because only unionized drugs are reabsorbed
57
what is enteral?
via the gastrointestinal tract
58
what is parenteral?
routes other than enteral
59
what is the first pass effect?
the loss of drug degraded during its first passage through the liver and intestinal wall after absorption from the GI tract
60
what is enterohepatic recirculation?
process by which drug metabolites are excreted in bile, then the parent drug is reabsorbed from the gut
61
how does enterohepatic recirculation affect a drug in the body?
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
what is the systemic dose equation?
the oral dose administered multiplied by the bioavailability (F)
63
how do you calculate bioavailability?
bioavailability (F) of oral= Area under the curve of oral divided by the area under the curve of IV
64
what should you think about with bioavailability?
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
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?
much less than 100%, maybe 50% or less
66
why are mathematical pharmacokinetics helpful?
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
the decrease in drug concentration is exponential-____________________________________________
a fixed fraction is lost with each unit of time
68
what does the distribution phase of the drug plasma concentration over time graph show?
the time where the drug is distributed to the tissues- an initial steep decline in concentration
69
what is half-life?
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
in five half-lives, over ____ of the drug is eliminated
95%
71
in ten half-lives, over ____ of the drug is eliminated
99.9% reference point for contamination of food products
72
what is apparent volume of distribution (Vd)?
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
what are the equations for calculating Vd and Co?
Vd=dose/Co=mg/kg/mg/ml=ml/kg Co=dose/Vd dose=Co x Vd
74
how do you calculate plasma concentration of a drug?
amount of drug in body divided by volume of distribution (ml) dose of drug (mg/kg) divided by volume of distribution (ml/kg)
75
does Vd indicate penetration into specific sites?
no
76
what is clearance (Cl)?
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
what makes up drug clearance?
hepatic clearance+renal clearance+other routes
78
what makes up drug elimination?
drug metabolism and drug excretion
79
at steady state, ________________ and __________________ are equal
rate of elimination and dosing rate
80
what is dosing rate?
dose of drug per unit time
81
what is the equation for clearance at a steady state?
rate of elimination/Css Css=average steady state drug concentration
82
what is the equation for clearance after a single injection?
Cl=dose/AUC AUC= area under the curve
83
clearance is _____________ of concentration of drug in the blood
independent
84
what is drug elimination?
amount of drug cleared from the blood per unit time Cl x drug concentration
85
clearance predicts the __________________________________________ in multiple dosing
average steady state plasma concentration
86
what is zero order kinetics?
drug elimination processes become saturated and a fixed amount is cleared per unit time can lead to overdose/more toxic effects
87
what is the slope of the drug concentration over time?
-k or Kel
88
what is the equation for half-life using the slope of the concentration over time graph
t1/2=0.693/Kel =0.693(Vd/Cl)
89
what are the primary parameters of pharmacokinetics?
volume of distribution and clearance half-life is the most useful secondary parameter
90
half-life is ________________ on Cl and Vd, but Cl and Vd are ________________
dependent independent
91
how long does it take to achieve steady state?
five half-lives time is independent of dosage
92
when will drug accumulation occur?
when dosing interval is less than 2 half-lives the shorter the interval, the more significant the accumulation
93
if the dosing interval is greater than ______________, accumulation of the drug is negligible
3-5 half-lives
94
why would we give a loading dose?
to reach therapeutic concentrations more quickly may still take 5 half-lives to reach stable steady state concentrations
95
what is the equation for loading dose?
loading dose= Vd x desired concentration
96
duration of drug action is extended by ______________ when the dose is doubled
one half-life
97
what does it mean for two drugs to interact with inhibition?
decreased elimination- toxicity
98
what does it mean for two drugs to interact with induction?
increased elimination- loss of therapeutic effect
99
when you change the formulation of a drug, does pharmacodynamics or pharmacokinetics or both change?
pharmacokinetics changes pharmacodynamics does not
100
what would impact blood flow to the site of absorption?
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
how prominent are changes in protein binding?
clinically significant effects relatively rare
102
what drugs interact with cytochrome P450?
Phenobarbital: induces Ketoconazole: inhibits
103
what is the first pass effect?
loss of drug degraded during its first passage through the liver after absorption from the GI tract
104
what is enterohepatic recirculation?
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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