Pharmacology definitions Flashcards
Pharmacodynamics is..
Are receptors important?
The action of the DRUG on the BODY. Receptors are KEY
Maximum response by the drug is otherwise known as-
Emax
EC50 is defined as…
The concentration of drug that produces 50% of the maximum effect.
Difference between Bmax and Emax…
Emax is the maximum response by the drug, whereas Bmax is the maximum number of receptors bound to drug
__ represents the concentration of free drug at which half maximal binding is observed. It characterises the receptor affinity for binding the drug in a reciprocol fashion.
Kd
If Kd is low, binding affinity is___
High
Define receptor-effector coupling
The process where the drug binds to receptor causing conformational changes and hence pharmacological response (ie coupling)
Coupling efficiency is determined by 2 factors…
- initial conformational change of the receptor
2. biochemical events that follow after coupling
T or F. ion channels produce a non-linear coupling response
F- linear
Drugs that bind to and mimic the regulartory effects of the endogenous signaling compounds are termed___
agonists
____ agonists bind to a different region on the R
Allosteric.
Difference between syntopic interaction, allosteric antagonism and chemical antagnoism and functional antagonism
Syntopic: competition with an agonist for the same or overlapping site on R
Allosteric: interacting with other sites on R
Chemical A: combining with the agonist to make it unavailable
Functional A: indirectly inibiting the cellular or physiological effects of the agonist
Define partial agonist
Only partly as effective as agonists regardless of the concentration
Define inverse agonists
drugs that stabilise receptors with background activity without an agonist, to render it inactive. Examples include: benzos, histamine, opioid, cannabinoid, dopamine, bradykinin, adenosine R.
Examples of nuclear receptors/lipid soluble agents (3)
steroid receptors, vitamin D, thyroid hormone
Tyrosine kinase receptor is an example of what class of physiological receptor
ligand regulated transmembrane enzyme
Insulin, growth factor act on what type of physiological receptor?
- GPCR
- Nuclear receptor
- TK transmembrane receptor
- intracellular enzymes
3
Define receptor down-regulation in TK receptors
Intensity and duration of actions of agents that act via TK receptors are limited by a process called receptor down regulation, where degradation of the TK-R occurs faster than the synthesis of the TK-R, hence the responsiveness to the ligands is diminished
Examples of ligand-gated ion channels
nicotine, gabapentin
Examples of voltage-gated ion channels
lidocaine, verapamil
cGMP has an establised signalling role in what 2 areas?
Intestinal mucosa and vascular smooth muscle
Define potency. Does it determine the clinical effectiveness or dose of a drug?
Concentration EC50 or dose ED50 required to produce 50% of drugs maximum effect.
Potency determines the DOSE.
Maximal efficacy is defined as… and is limited by__
maximal response produced by the drug, and is limited by the drugs toxic effect
__50 is defined as a dose at which 50% of individuals exihibit the specific quantal effect
ED 50- median effective dose
Define LD50
Median lethal dose required at which 50% of individual die if given a specified dose
Tolerance vs tachyphylaxis
Tolerance: responsiveness decreased with continued administration
Tachyphylaxis: responsiveness diminishes rapidly after given a drug
What is the equation for Vd
Vd= amount of drug in body/Conc
What is the equation for Clearance?
Cl= rate of elimination / Conc
ETOH clearance is an example of __-order elimination
Zero order
rate of drug elimination is directly proportional to the concentration= __-order elimination
First order
Clearance= dose/AUC describes what order elimination?
First order
When elimination becomes saturated and becomes constant despite increasing levels of drug concentration- this is called __-order elimination?
Zero order
Rate of elimination = Vmax x c / Km+C
Describes what order elimination?
What does Vmax and Km stand for?
Zero order
Vmax: maximum elimination capacity
Km- when elimination is 50%
Define half life
Time required to change the body concentration of drug by half during elimination
T1/2 = 0.7Vd / CL
How many half lives does it take to eliminate 50% of the drug? How many half lives for 75%
1 half life; 2 half lives to eliminate 75%
Describe what the AUC represents
AUC is proportional to the extent of bioavailability for a drug is its elimination is first order.
Define first pass elimination
portal blood and metabolism by live/excretion into bile
