Pharmacodynamics: This is the study of “what the drug does to the body.” It includes how drugs act on receptors and the effects they produce, dose-response curves, and related topics.
Mechanisms of drug action: Drugs can work in several ways, including:
Some drugs act as chelating agents or osmotic diuretics. A single drug may use more than one of these mechanisms.
| Type of drug | Characteristics | Examples |
| Agonist | Drug binds to a receptor and produces the desired response. | Epinephrine binding on beta 1 receptor increases heart rate |
| Antagonist | Drug binds to a receptor and prevents an agonist from binding to the receptor; antagonists do not themselves have inherent activity on the receptor | Propranolol binding to beta receptor prevents epinephrine binding to beta receptor so that epinephrine is not able to increase heart rate |
| Partial agonist | Drug binds to a receptor but produces a smaller effect than a full agonist acting on the same receptor. | Buprenorphine on opioid receptors; Beta blockers with intrinsic sympathomimetic activity like pindolol, acebutolol; aripiprazole on dopamine receptors |
| Inverse agonist | Drug binds to a receptor and produces the opposite response of an agonist. For example, if agonist binding increases heart rate, then inverse agonist binding decreases heart rate. In contrast, antagonist binding prevents the heart rate from increasing, but it would not decrease it below baseline. In the presence of an agonist, the inverse agonist behaves like an antagonist. | Carvedilol on beta receptors, naloxone on opioid receptors |
An antagonist can inhibit the actions of both agonists and inverse agonists.
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