Pharmacodynamics (Chapter 3) Flashcards
what is the difference between pharmacodynamics and pharmacokinetics ?
pharmacokinetics: how the body acts on the drug
pharmacodynamics: how the drug acts on the body
what is an agonist ?
a ligand that binds to a receptor and initiates a change in the cell via a transduction mechanism
what is an antagonist ? give an example.
a ligand that binds to a receptor but does not initiate a change in the cell- it has no function. It blocks the endogenous compound, like a “blocker”
beta-blocker
what is a site of action ?
specific molecular surface on the target, usually a receptor, where the drug binds
what is the onset of action ?
the time it takes for the concentration of a drug at the site of action to be large enough to cause a response.
what is the duration of action ?
time between onset and termination of action, the time the drug produces the effect.
what is receptor theory?
most drugs interact with a receptor- agonist brings a productive change to the target cell, antagonist brings an unproductive change to the target cell.
what are the three places where you can find receptors on a cell?
on cell surface
in cytoplasm
in nucleus
where do most protein-based drugs bind to receptors ?
on cell surface
where do most lipid-based drugs bind to receptors ?
cross the membrane
what kind of reaction does NE and E binding to an alpha-1 receptor bring ? by what pathway?
PIP2 cleavage by phospholipase C produces second messengers IP3–> produces Ca2+ –> smooth muscle contraction
and second messenger DAG
what kind of reaction does NE and E binding to an alpha-2 receptor bring ? by what pathway ?
inhibits the release of NE and E by negative feedback
inhibits adenylyl cyclase, provoking smooth muscle contraction
what kind of reaction does NE and E binding to a beta receptor bring ?
ATP goes to cAMP thanks to adenylyl cyclase
heart muscle contraction, smooth muscle relaxation, glycogenolysis
draw a graph which shows the plasma concentration of a drug over time
I . peak concentration.
I . .
I . .
I . .
I . . minimum effective concentration
I . .
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
I duration of I
I action I
onset termination
half-life: in the middle of the duration of action
the curve that shows the plasma concentration of a drug over time- how would you explain to an athlete, using this graph, why they shouldn’t take too much pain medication ?
either you have pain or you don’t. there isn’t such a thing as “feeling less pain”. When the curve increases, you’re not “feeling less pain”, and taking more of a drug won’t increase the effect. An increased dose would be for an increased duration of action, not for a better treatment.
explain how the beta-1 receptor works on the heart.
funny current controls heart rate.
Stimulation of myocardial beta-1 receptor shift activation of the If current to less negative voltages. This causes faster diastolic depolarization and heart rate.
what is single-dose response ? explain the pharmacodynamics
when the drug is taken once in a large quantity (bolus).
concentration of drug increases and more and more receptors are occupied until all are occupied.
what happens if you take more of a single-dose response drug than you’re supposed to?
useless, since all the receptors are taken up. more drug will not have more of an effect. extra medication will be metabolized and excreted, and may lead to kidney and liver damage.
what is a multiple-dose response ? what is its advantage
it’s a way to extend duration of action but won’t exceed peak value (reaches steady state)
rate of the drug becoming bioavailable is equal to the amount being excreted
what happens if someone takes more than you’re supposed to of a multiple dose drug ?
exceeds peak and then crashes (risk of toxicity)
may even make the effect lower due to desensitisation
how many half-lives does it take for a multiple dose drug to get to steady state ?
4-5
what is a loading and maintenance dose ?
a type of multiple dose where first a large bolus of loading dose is taken to get to peak and then lower maintenance doses are taken frequently after to keep the drug at steady state.
how is loading and maintenance dose different from a single dose response ?
the loading dose and subsequent maintenance dose are calculated differently.
what is ED50?
an effective dose
what is an effective dose (ED50)?
amount of drug needed to produce a therapeutic outcome in 50% of the population (potent effect). a lower dose would then be considered a stronger drug.
what is LD50?
lethal dose
what is a lethal dose (LD50)? how is it calculated ?
amount of drug needed to kill half the population
extrapolated from animals
what is TD50?
toxic dose
what is a toxic dose (TD50)?
amount of drug that produces a specific toxic effect in half the population eg tinnitus
what is the therapeutic index ?
TD50/ED50 or LD50/ED50
the higher the TI the safer the drug.
what is the rationale behind the 50% in LD50 and the other safety terms?
no real rationale, just a set point
what is the TI of THC? what does that mean ?
TI of 1000:1, considered very good
what is the TI of morphine ?
70:1
pretty bad, more risk and less reward
what is the TI of cocaine ?
15:1
bad
what is the TI of ethanol?
10:1
bad
between a red liquid LD50 0.1 ng and blue liquid LD50 150 g, which one is safer ?
blue, because a higher amount is needed to be lethal
Which drug is the best investment between :
A, ED50 100mg/kg
B, ED50 0.1 mg/kg
B, because you need less of it for it to be effective therefore it is stronger
A would be more costly to make and increase chances of adverse effects
what are four things that affect compliance ?
cost
forgetting
inconvenient (insulin, inhaler)
education
what are two ways to improve compliance?
medications that can be taken less times per day
patient education
