Full Agonist Vs Partial Agonist

As discussed in previous article, an agonist is a molecule that causes a physiologic response when it binds to its receptor.

A drug can be classified as Full agonist or Partial agonist depending on its efficacy.

Let’s Say Drug A is the Full agonist and Drug B is the partial agonist.

So, how both can be agonists and have different magnitude of action?

A full agonist can be effective 100% although not all receptors are occupied. This means that Drug A needs less than 100% of the receptors to result in full response.

On the other hand, drug B, a partial agonist will never be able to reach 100% even if it occupied 100% of the receptors present.

This happens because the physico-chemical properties of the full agonist that allow it to make a bond with the receptor in a way that it can excite only 3 receptors (theoretically) to result in 100% of the effect.

The physico-chemical properties of the partial agonist allow it to bind to its receptor, however, with lower ability to excite it and produce the desired response, even with occupying 100% of the receptors present.

Examples of full agonists are morphine, opium and phenylephrine. Buprenorphine and Tolazoline are examples of a partial agonist.

You can also watch the illustrative video below for more understanding of the topic.