W2: Tachyphylaxis and desensitization Flashcards
What happens when there is repeated exposure of ligands to receptors?
Tachyphylaxis and desensitization will occur
What is tachyphylaxis?
It is the downregulation of receptors, basically the reduction in the amount of receptor expressed.
Tachyphylaxis happens due to the __________ exposure to ________.
continuous exposure to agonist (drug).
Unlike tachyphylaxis that develops ________, desensitization takes ___________ time.
tachyphylaxis develops quickly (acute) but desensitization takes a much longer time
The response to tachyphylaxis is by _______ of receptors.
Upregulation, which means the they synthesize more receptor to overcome the chronic receptor antagonism.
This happens quickly just after downregulation.
Desensitization = _______
tolerance, gradual decrease in responsiveness
There are two mechanisms of desensitization, what are they and explain.
- Changes in receptor conformation = e.g. receptor phosphorylation so that the receptor cannot respond to ligand
- Downregulation of receptor = by internalization of receptors through endocytosis
Why does tachyphylaxis and desensitization occur?
Because the amount of receptor is not constant and will adapt as the drug is given repeatedly
Basically the receptors are used to the drug so it will be less sensitive = less desired effect
Toxic side effects (TD50) and __________ are both dose dependent.
Toxic side effects (TD50) and lethal effects (LD50) are both dose dependents.
How would a pharmacist know if a drug is safe to use?
Look at the therapeutic index lah
Formula for therapeutic index =
TD50 / ED50 = T.I
As paracelsus once said “poison is in everything and no thing is without poison. _____”
“poison is in everything and no thing is without poison. The dosage makes it a remedy and a poison”
Why should we care about therapeutic index?
because it tell us how safe a drug is and how much dose we need to administer.
A drug with small T.I is unsafe because the dosage for therapeutic effects might overlap to produce toxic side effects.
In this case, the bigger the better.
