Pharmacology Questions


Can anyone explain what a therapeutic range is? Also the difference between antagonist and agonist. My professor and our textbook don't do a good job of describing both so I'm a little bit confused.

allnurses Guide


3 Articles; 5,581 Posts

Specializes in Adult Internal Medicine. Has 12 years experience.

In very simple terms:

Therapeutic range is the level range of the drug in the blood that produces its intended effect without toxicity.

Agonists cause the receptor to fire. Antagonists prevent the receptor from firing.


5 Articles; 404 Posts

Specializes in Hem/Onc/BMT. Has 11 years experience.

To expand a bit more on agonists/antagonists...

Receptors are basically big proteins in cells that bind with various signalling molecules and carry out various functions. An agonist binds or stimulates the receptor, which causes a cascade of cellular reactions to bring desired effect. An antagonist does the opposite; it prevents the receptor from binding its ligand, in effect inhibiting the receptor's function.

Take epinephrine, for example. This hormone binds various receptors and bring about the "fight or flight" response. One of the receptors it binds is beta 1 receptor, whose target effect is the heart. There are drugs that mimic this effect -- dobutamine is a beta 1 agonist that increases cardiac output. Beta-blockers like metoprolol, on the other hand, are beta 1 antagonist that decreases BP and HR.

Another example is opioid receptors in the brain. When these receptors are stimulated, it blocks sensation of pain and cause euphoria. Morphine is an agonist that binds these receptors. Naltrexone, on the other hand, is an antagonist of opioid receptors and used for treating narcotic dependency.

So you can see, agonists and antagonists are drugs that often bring opposite effects by way of stimulating (agonist) or inhibiting (antagonist) the target receptor.


32 Posts

Thanks so much for the explanations -- sometimes it helps a lot to hear things worded differently!

One more question, is the therapeutic range the same as the therapeutic index?