Question

Select a drug example for each the agonist, partial agonist, antagonist, and inverse agonist and explain if the resultant action is fast onset (seconds to minutes) or slow onset (weeks) and how do you know?

How could environment effect response to these drug examples?

Answer 1

An agonist is a chemical that binds to a receptor and activates the receptor to produce a biological response. Agonist causes an action, antagonist blocks the action of the agonist and an inverse agonist causes an action opposite to that of the agonist.

Example

Agonist: Opioid analgesics

Antagonist: Naloxone

Inverse agonist: Naltrexone

Full agonists bind tightly to the opioid receptors and undergo significant changes to produce maximal effect.   Examples of full agonists include codeine, fentanyl, heroin, hydrocodone, methadone, morphine, and oxycodone.

Partial agonists cause less changes and receptor activation than full agonists. At low doses, both full and partial agonists provides similar effects. However, when the dose of partial agonists increases, the analgesic activity will plateau, and further increases in doses will not provide additional relief but may increase the adverse effects. Examples of partial agonists include buprenorphine, butorphanol, and tramadol.