• To explain the concept of efficacy

efficacy is the efficiency that a drug can activate, efficacy is greater if the drug uses fewer receptor active sites to reach maximum response of the tissue. (maximum response is achieved when stimulus that is expected is generated by receptor-drug interactions)

• To apply the concept of efficacy to drug-receptor interactions

Very efficacious drugs will require to occupy fewer

receptors to give a response

than less efficacious ones

• To identify the 2 properties of drugs interaction with receptors

Affinity - is a measure of the concentration range over which a drug binds to its receptor (how attracted a drug is)

Ka- directly proportional

Kd - indirect (low Kd = high affinity)

Pa2 = directly proportional only for competitive antagonists

• To recognise the difference between competitive and non-competitive antagonists

competitive - can be irreversible or reversible, sits in the active site of a receptor and prevents an agonist from binding, if they are non-reversible they can only be outcompeted for a short period of time

non-competitive - examples of allosteric modulation the antagonist blocks access of the agonist to its binding site thru steric hinderance

this picture shows a irreversible competitive antagonist