Part 5 Flashcards
Efficacy
Ability to produce maximal effect
Full agonist
Has enough efficacy to produce maximal effect even at less than 100% occupancy of receptors eg phenylephrine in contraction of isolated strip of rabbit aorta
Partial agonist
Produces submaximal effect even at 100%occupancy and has intermediate efficacy eg tolazoline , oxymetazoline
* partial agonist with low efficacy is an antagonist cause it prevents the agonist from binding to the receptor and activating it
Emax
Measure of efficacy of drugs to cause maximal response
Neutral antagonist
Zero efficacy and no effect on tissue
Name a highly potent opioid full agonist
Fentanyl
Potency
The power a drug has and is measured by the concentration of a drug required to reach maximal effect
Potency vs efficacy
Potency- C50 cause potency is concentration
Efficacy - Emax cause efficacy is effect
Drug antagonism
When effect of one drug is reduced in presence of another
Chemical antagonism
When 2 substances bind in solution and the effect of the active drug is lost
Example of chemical antagonism
Chelating agents eg dimercaprol which binds to heavy metals like arsenic, gold, mercury, lead and copper and reduces their toxicity
Adalimumab
Anti rheumatoid drug and binds to tumour necrosis factor alpha which causes inflammation
Example of pharmacokinetic antagonism
Digoxin specific antibody Fab fragments bind to digoxin molecules and neutralises them
Examples of synergistic drugs
Ethanol, morphine
Examples of additive drugs
Codeine , ibuprofen
Synergism
When 2 drugs are added together their total effect will be greater than the sum of their individual effects
What is required for a drug to be useful as a therapeutic agent
The drug should act selectively on receptors of particular cells
Examples of tricyclic antidepressants
Imipramine,nortriptyline
Actions of tricyclic antidepressants
Block ( monoamines)noradrenaline and serotonin reuptake transporters
Block muscarinic and a adrenoceptors that cause unwanted effects like dry mouth (antimuscarinic), sedation (anti Ha1 ) orthostatic hypertension (anti- a adrenergic
Quantal dose response relationship
Describes a drug effect that is binary (present or not present)
Eg either death or hypnosis
Quantitative response
A response that is quantified by quantitative variables
Therapeutic index
Ratio of median lethal dose to median effective dose in animals
Therapeutic index humans
Ratio of Median toxic dose (TD50) to ,Edina effective dose (ED50)
Therapeutic window
Lies between 2 regions of exposure associated with therapeutic failure
Differentiate between lower region of failure and upper region of failure
Lower- inability to have adequate efficacy
Upper- inability to have adequate efficacy without an adverse response
