04- Potency, Efficacy and Therapeutic Index Flashcards
pharmacodynamics
the study of how drugs interact in the human body
true or false: all patient reacti the same to medications
false: Patient response to medications are highly individualized
2 types of studies of pharmacodynamics
- quantal effects
2. graded effects
frequency distribution curve
a graphical representation of the number of patients responding to a drug action at different doses (quantal)
dose-response curve
Plot of data showing effects of various doses of a toxic agent on a group of test organisms (graded)
quantal effects use what type of patient questions
yes/no (ex. did drug reduce BP by 20mmhg?)
do frequency distribution curves indicate magnitude/max effect of drug dose?
no.
Median effective dose (ED50)
the dose of a drug that produces a therapeutic response in 50% (refered to as standard dose)
therapeutic index
Ratio of a drug’s LD50 (or TD50) to its ED50
median lethal dose (LD50)
The drug dose that causes death in 50 percent of the experimental animals in which it is tested.
Median toxic dose (TD50)
The drug dose that produces a specific adverse (toxic) response in 50 percent of the patients in whom it is tested.
quantal
saftey of a drug
LD50/ED50 = # client would have to increase dose #’s before seeing specific adverse effect on average
ex. which drug is safer? a drug with a quantal number 4 for increased HR as the adverse effect or a quantal number of 2 with an adverse effect of increased resp.
drug A - up to 3x dose without adverse effect, on average
why is the quantal number so important? which demographic?
elderly patient often forget and double dose. the higher the quantal number, the larger the therapeutic window, the safer the drug :)
therapeutic window
Range based on minimum effective therapeutic [ ] and minimum toxic [ ] for specific toxic effect
high alert medications are:
medications with very low therapeutic windows that effective and toxic dose ranges overlap
true or false: approx. 40% of patients need higher drug doses to reach desired effects
false: 25%
dose-response curve
Demonstrates magnitude of biological response to a drug
Obtained by observing and measuring patient responses at different doses of drug
dose response curves are used to determine:
therapeutic range
efficacy
potency
3 phases of dose response curve
- few cells affected (not enough, little effect)
- linear relationship between amount administered and degree of response
- plateau - increasing dose has no effect (possible adverse)
potency
Compares doses of 2+ drugs w respect to how much drug is needed to produce a specific response
usually based on median effective dose or concentration (ED50)
efficacy
ability of drug to help client (exert more of a therapeutic response)
what is a more important factor when assessing which drug is “better”: potency or efficacy
efficacy
true or false: highly potent = lower affinity to receptor?
false
association
drug binds to its receptor (k1 = Rate of drug-receptor complex formation)
dissociation
k-1 = rate occurrence
if k-1 is faster than k1 what does this mean in relation to association and dissociation and the drug’s affinity to a receptor?
association < dissociation
low affinity for receptor
dissociation constant (Kd)
a measure of the affinity of the receptor for its ligand
k-1)/(k1
true or false: a drug’s affinity for a receptor tells us how well drug binds to receptor and the action of the drug at the receptor
false: Doesn’t tell us anything about action of drug at receptor
types of agonists:
Full, partial, inverse
types of antagonists
reversible, competitive, non-competitive, and irreversible antagonists
when do you use agonists vs. antagonists
agonist: if not making enough of ligand (replacement)
antagonist: too much of ligand or hormone
Full agonist
Ability of a drug to produce 100% of the maximum response regardless of the potency
same effect as ligand (ex. dexamethasone for adrenal insufficiency)
partial agonist
a drug that binds to a receptor and causes a response that is less than that caused by a full agonist (ex. aripiprazole for dopamine and management of bipolar or schizophrenia)
true or false: efficacy of full agonist will always be higher than partial agonists
true
inverse agonists
Bind to same receptor site as natural ligand, but induce opposite response to endogenous ligand (ex. GABA receptor. agonist have sedative response but inverse agonists have anxiogenic effects)
when are inverse agonists viable?
Only occurs when receptors have an intrinsic (basal) level of activity
true or false: inverse agonists have negative efficacy
true
antagonist
bind to same receptor site ad endogenous ligand, but do not produce same effect (no efficacy)
types of antagonists
reversible (competitive and non-competitive) and irreversible
competitive agonist
Antagonist competes for same receptor binding site as endogenous ligand (linear drug response)
non-competitive antagonist
binds to an allosteric (non-agonist) site on the receptor to prevent activation of the receptor
clinical quality of non-competitive antagonists
poor. hard to predict response curve
allosteric modulation
binding to another site on a receptor
irreversible antagonist
A pharmacologic antagonist that cannot be overcome by increasing agonist concentration
what does it mean for an irreversible antagonist to have its rate of dissociation (K-1) be 0?
Kd will be very low and its affinity to the receptor is very high
ex. of irreversibel antagonists
biological weapons: Cholinesterase inhibitors (“nerve gases”)
drugs: Aspirin, omeprazole (management of GERD)
