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what is "pharmacodynamics"? what is "biotransformation"?
- pharmacodynamics - how drugs exert their effect.
- biotransformation, or metabolism - how the body alters a drug.
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list the 2 main categories of pharmacodynamics.
receptor mediated actions, non-receptor mediated actions.
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what is the receptor mediated action?
the drug exerts its effect because its molecules combine with a receptor on a cell membrane, causing that cell to do something.
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what is a non-receptor mediated action?
the drug exerts its effect in some way that does not involve a recepter
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what is a receptor?
specialized protein molecule on the cell membrane of a target cell that is particular molecule - drug, hormone, neurotransmitter - "fits" into - which may cause an effect (contract, secrete, initiate a new nerve impulse) prevent an effect (inhibitory), or have no effect (antagonist).
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what is "intrinstic activity"?
the ability of a drug to produce an effect
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when a drug with intrinsic activity combines with receptor, what happens?
an effect is produced, such as causing something to happen or preventing something from happening (agonist)
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when a drug with no intrinsic activity combines with a receptor, what happens?
no effect is produced. the cell proceeds as if nothing were occupying the receptor. (antagonist). this drug with no intrinsic activity does prevent an agonist from occupying the receptor.
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what is an agonist?
a drug with intrinsic activity
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what is an antagonist?
a drug with no intrinsic activity
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what is competitive (or reversible or surmountable) antagonism?
when both an agonist and antagonist drug are present, both compete equally for receptors, so whichever is present in a higher concentration produces the most effect (or lack thereof).
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when is competitive antagonism useful clinically?
when you want to reverese the effects of an agonist drug such as xylazine, you give the patient the antagonist drug - in this case, yohimbine
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what is a partial agonist/antagonist?
a drug with little intrinsic activity - given by itself, if has a small effect. given a full agnoist, it will reverse most of the full agonist's effect
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what is non-competitive (or irreversible or insurmountalbe) antagonism? is it really irreversible?
in competing for receptors, the antagonist has the advatage - it has more affinity for the receptor, or changes the shape of the receptor so the agonist cannot fit into it anymore. the antagonist "wins". it is not really irreversible - it just takes a long time or a lot more of the agnoist drug to reverse.
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what is a non-receptor mediate action? give 3 examples
when a drug has an effect in a patient that does not involve a "drug + receptor = action" effect. for example: osmotic diuresis, chelation, direct chemical change
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what is biotransformation, or metabolism?
the process by which enzymes in the body change drugs into different compounds, which are called metabolites.
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what is the amin site for biotransformation in the body?
the liver
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name 4 types of chemical reaactions taht enzymes may drive to biotransform drugs
oxidation, reduction, hydrolysis, conjugation
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briefly describe the chemical reaction "conjugation".
addition of glucuronic acid molecule to the drug molecule - the resulting molecule is dydrophilic, easier to excrete in the urine
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what is a metabolite?
when enzymes change the original drug into different compounds, they are called metabolites. end products of biotransformation
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do these metabolies usually have more or less activity than the original drug?
less
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are metabolites usually easier or harder to excrete than the original drug? why?
easier. more hydrophilic, less protein-binding.
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what happens to the rate of metabolism of 2 drugs when they are both administered in to the patient at the same time and they both use the same enzyme system for biotransformation?
the rate is slowed down - "bottleneck" effect
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what is "induction"?
increased rate of biotransformation caused by repeated use of certain drugs
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does an induced enzyme system metabolize drugs faster or slower than usual?
faster
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can an induced enzyme system increase the rate of metabolism of a drug other than the drug that originally induced the system?
yes - if the second drug uses the same enzyme system for biotransformation
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if you are using a drug in a patient that has caused induction of its enzyme system, will you need to increase or decrease the dose of the drug over time to maintain the same effect?
increase
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what is drug "tolerance"?
with continued use of the same dose the drug, the patient shows decreased effect
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as a patient develops tolerance to a drug, what do we have to do to the dose of the drug to maintain the desired effect in the patient - increase or decrease the dose?
increase
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do all species metabolize all drugs the same?
no
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in general, which species is less able to metabolize certain drugs - dogs or cats? why?
cats - have reduced ability to form glucuronic acid, so they cannot conjugate drugs for excretion as well.
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in general, do neonatal and geriatric patients metabolize drugs faster or slower than young adult patients?
slower
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in general do neonatal and geriatric patients need higher or lower doses of drugs than young adult patient?
lower
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can malnutrition affect drug metabolism? will malnutrition speed up or slow down metabolism and excretion? why?
yes. slow down. lack of amino acids to make new enzymes.
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can liver disease affect drug metabolism? will liver disease speed up or slow down metabolism and excretion? why?
yes. slow down. less capable of making new enzymes
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