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What is “pharmacokinetics”?
the study how a drug moves into, through, and out of the body.
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Why do we have to learn about pharmacokinetics?
because changes in the state of the patient can alter how a drug moves in the patient’s body – can lead to subtherapeutic or toxic drug levels – we may need to alter dose and dose interval to maintain the therapeutic level.
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What
are the 4 main stages of pharmacokinetics?
absorption, distribution, metabolism, excretion (elimination).
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What does “absorption” of a drug
refer to?
movement of the drug from the site of administration into the systemic blood circulation.
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Why does a drug need to get into
the systemic circulation of a patient?
so that it can travel – be distributed – to the site where it acts – where it is needed.
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What is “bioavailability”?
what percentage of the administered drug gets into the blood, expressed as a decimal. ex: 60% = 0.6
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What
is the bioavailability of a drug administered by the IV route?
1.0
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Is the bioavailability of any drug
not given IV greater than 1.0 or less than 1.0, and why?
less than 1.0 – because the drug has to cross cell membranes and diffuse through tissue fluid to reach the capillaries – it does not all get into the blood at once. as time goes on and more drug gets into the blood, some of the drug will already have been removed from the blood by the liver and kidneys, therefore all of the drug will never be in the blood at the same time.
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Does route of administration affect
how fast the blood concentration of a drug peaks?
yes
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A drug given by which route of administration peaks fastest?
- IM or SQ – IM is fastest.
- PO or IM – IM is fastest.
- IM or IV – IV is fastest.
- IV or PO – IV is fastest.
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Which route of administration would
be best for administering drugs during an emergency (CPR) –IV, IM, SQ, or PO?
IV
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List the 4 ways that drug particles
can move during absorption. Which is most common?
passive diffusion (most common), facilitated diffusion, active transport, pinocytosis/phagocytosis.
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What is passive diffusion?
movement of drug particles from an area of high concentration to an area of low concentration.
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Is energy (ATP) used by the body to achieve diffusion?
no
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What is the difference between
passive diffusion and facilitated diffusion?
both are movement of particles from an area of high concentration to an area of low concentration, and both do not use energy (ATP). in facilitated diffusion, carrier molecules in cell membranes help molecules to cross the cell membrane, at a faster rate than passive diffusion.
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Is energy (ATP) used by the body to
achieve facilitated diffusion?
no
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Is facilitated diffusion an active
or a passive process?
passive
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What is active transport?
molecules are actively pumped or carried, using carrier molecules and ATP, across a cell membrane, from an area of low concentration to an area of high concentration - opposite of passive diffusion.
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Is energy (ATP) used by the body to achieve active transport?
yes
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Carrier molecules are involved in
what 2 types of drug particle movement?
facilitated diffusion and active transport.
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What are pinocytosis and phagocytosis? Are these mechanisms for moving drugs across cell membranes common or rare?
pinocytosis – “cell drinking” – cell membrane actively engulfs drug molecule. phagocytosis – “cell eating” cell membrane actively engulfs larger drug particle. these are rare in drug transport.
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What happens to the rate of facilitated diffusion or active transport when carrier molecules are saturated?
rate of transport is limited – “bottleneck” effect.
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Does the blood supply to the site
of administration of a drug affect the drug’s rate of absorption?
yes
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What do we mean when we say that a
tissue is “well perfused” or “poorly perfused”?
well perfused tissue has a good blood supply. poorly perfused tissue does not have as good of a blood supply.
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Which tissue normally is the most
well perfused – muscle or fat?
muscle
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Which tissue normally is the most
well perfused – exercising muscle or resting muscle?
exercising muscle
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From what location will an
injection be absorbed into the circulation the fastest – from muscle or fat?
muscle
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A drug normally well absorbed when
given PO is given PO to a very frightened patient. Do you expect this drug to be absorbed at the same rate as usual, faster than usual,
or slower than usual? Why?
slower – less movement and blood supply to the GI tract when under the influence of sympathetic stimulation.
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A drug normally well absorbed when
given IM is given IM to a patient in shock. Do you expect this drug to be absorbed at the same rate as usual, faster than usual, or slower than usual? Why?
slower – because a patient in shock has lower blood pressure and more poorly perfused tissue than usual.
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What does “lipophilic” mean?
fat-loving
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What part of the body does a
lipophilic drug dissolve into fastest and most easily?
lipophilic drugs dissolve into lipid structures: fat, lipid cell membranes, brain.
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Which of the following does a
lipophilic drug passively diffuse through the most easily – lipid cell membranes or watery tissue fluid?
lipid cell membrane
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Is a lipophilic drug absorbed more
easily if given PO or if given IM?
PO – crosses cell membranes of cells lining the GI tract.
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Are lipophilic drugs ionized or
non-ionized?
non-ionized.
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What does “hydrophilic” mean?
water loving
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What part of the body does a
hydrophilic drug dissolve into fastest and most easily?
hydrophilic drugs dissolve into water: tissue fluid, plasma, etc.
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Which of the following does a
hydrophilic drug passively diffuse through the most easily – lipid cell membranes or watery tissue fluid?
watery tissue fluid
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Is
a hydrophilic drug absorbed more easily if given PO or if given IM?
IM
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Are
hydrophilic drugs ionized or non-ionized?
ionized
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In general, what is a
“fenestration”?
a gap or hole
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In
reference to capillaries, what are fenestrations?
gaps between the endothelial cells lining capillaries.
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Why are these fenestrations in
capillaries important in drug absorption?
hydrophilic drugs cannot enter capillaries by crossing the cell membranes of the endothelial cells (unless they use a carrier protein – facilitated diffusion or active transport), but they can enter by passing through fenestrations.
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