Pharmacodynamics Flashcards
Define pharmacodynamics
The study of the interaction between a drug and its molecular target and of the pharmacological response
"What the drug does to the body"
Define drug target interactions
Drug target interactions
An interaction with a drug and its target has different classifications depending on the type of molecular target
In general when a drug binds to its target something will happen or stop happening…leading to a physiological outcome.
Define agonists
Binding of a drug to receptor causes a functional response, the response is determined by drugs affinity to receptor
Can be full or partial depending on the ability to elicit a response
Partial agonists bind to and activate receptor:
They are unable to elicit the same maximal response as an endogenous ligand even when all receptors are occupied.
In the presence of a full agonist they will reduce the effect of the full agonist as they occupy the receptors acting as competitive antagonists (reducing the availble binding sites of the full agonist)
Can be direct or allosteric agonist depending on the binding site
Define antagonists
Antagonists
Bind to receptor without eliciting a response, preventing binding of an agonist (and therefore preventing activation of the receptor)
Can be:
Competitive reversible antagonists
Interfere with the binding of endogenous agonists – compete for receptor sites
Can be overcome by ↑ agonist
No effect on efficacy (but does reduce apparent potency)
Competitive Irreversible antagonists
Limited therapeutic use
Permanently make receptor unavailable for agonist to bind to
Generally a reduction in efficacy (with or without a reduction in potency)
Non-competitive antagonists
Block response to an agonist at some point within the cascade of intracellular events
↓ maximal response of agonist
Descibe the types antagonist
- competitive
- non competitve: reversible and irreverisible
Describe efficacy, potency and affinity
Affinity describes strength of drug binding (occupation) with receptor (“fit the lock”).
Potency is the amount of drug required to elicit a response.
Efficacy describes ability of drug-bound receptor to produce a response or be activated (“turn the key”).
Agonists have both affinity for the receptor AND efficacy but antagonists have affinity but NO efficacy.
How does efficacy and affinity play a role in the action of agonists and antagonists?
Agonists have both affinity for the receptor AND efficacy but antagonists have affinity but NO efficacy.
- COMP ANTAG: effects on potency of agonist, not efficacy ie reaches max, but slower
- IRREV NONCOMP: can have an effect on potnecy, and does affect efficacy, cant reach max
- REV NONCOMP: effects on efficacy not potency
Define potency
How much drug is required to have an effect. (increasing potency shifts the red curve to the left)
Describe efficacy
How much of an effect will the drug have when all targets are occupied
What does EC50 describe?
Potency
What does Emax describe ?
Efficacy
Define therapeutic index
Quantitative measurement of the ratio of the lethal dose of a medication and the effective dose of that drug
eg TD50/ED50
Large TI: wide window
Define therapetic window
A term used to describe the therapeutic index
"wide" indicating a large ratio between efficacy and lethal dose "narrow" indicating a small ratio between efficacy and lethal dose
TRUE or FALSE - all patients will experience some therapeutic effect within the therapeutic window
FALSE: some may not experience therapeutic effect. some may experience side effects - ie zig zag way above or way below
Describe tolerance
Decreased response of receptor to drug over tim with repeated use
Can be plotted as clockwise hysteresis loops
acute tolerance is also known as tachyphylaxis
e.g. anti-deps, opioids
