receptor mechanism

Question 1

what are the three interactions with the drug and its target

Answer 1

• drug receptor interaction
• drug enzyme interaction
• drug and DNA interaction

Question 2

how can drugs interact with their target

Answer 2

• covalent interactions (irreversible)
• e.g. overdosing in paracetamol can cause it to be converted to a toxic metabolite (NAPQI) which forms covalent bond with proteins in the liver causing necrosis and severe drug induced liver injury
• reversibly via London forces, ionic bonds, hydrogen bonds (drug target complex dissociated easily)

Question 3

what type of bond does aspirin form and what molecule is its target

Answer 3

• covalent interactions
• enzymes are its target

Question 4

what is the mechanism of pesticides

Answer 4

• covalently bind to AchE (which breaks down Ach)

Question 5

what is the law of mass

Answer 5

rate of reaction (drug and receptor combining to form drug-receptor complex) is proportional to the concentration of the reactants

Question 6

what is affinity

Answer 6

how readily the specific ligand binds to the receptor

Question 7

what is the ec50 and its relationship with potency

Answer 7

EC50 is the concentration of the drug which provides effect to 50% of individuals or the concentration of the drug which produces 50% of the maximal affect
the greater the potency the lower the EC50

Question 8

What is the relationship between increasing the dose of the drug and the effect

Answer 8

• at very low concentrations increasing drug dose would still have no impact on drug effect/outcome
• at higher concentrations/doses increasing the dose would increase the effect however after a certain point increasing concentration/dose has no impact on the effect/outcome

Question 9

what are the two ways a drug can interact with its target/receptor

Answer 9

• agonist (activate the receptor)
• antagonist (has no impact on receptor, prevent binding of agonist, so antagonist have zero efficacy)

Question 10

what are the two types of agonist

Answer 10

• full agonist= provide a maximum efficacy/ maximal response
• partial agonist= do not provide a maximal response e.g. opioids are useful cough suppressants and a partial agonists
• morphine is a full agonist and can be too dangerous

Question 11

what is an example of an partial agonist

Answer 11

pholcodine (opioid cough suppressant) is a partial agonist with lower efficacy that morphine so is safe for unsupervised administration

Question 12

how does antagonists work

Answer 12

block activity of receptors, prevent binding of agonist
has an efficacy of zero, no response is produced

Question 13

what are the 3 different types of antagonists

Answer 13

• reversible competitive antagonists
• irreversible competitive antagonists
• non competitive antagonists

Question 14

how does competitive reversible antagonists work

Answer 14

• compete with the agonist to bind to the orthosteric site of the receptor- prevent agonist from binding
• binding is reversible
• effects of reversible competitive antagonists are overcome by increasing the concentration of agonist
• many drugs are competitive reversible antagonists
• potency of agonist is reduced but maximal efficacy is not changed
• dose response curve shifts to the right (extent of shift dependant on concentration of antagonist and affinity of antagonist)

Question 15

how does irreversible competitive antagonists work

Answer 15

• again prevent agonist binding
• irreversible so binds to covalently and therefore new receptors need to be made to overcome effect
• efficacy reduced

Question 16

how does non competitive agonists work

Answer 16

bind at distant site not the agonist binding site, efficacy reduced