Agonist

Definition

An agonist is a pharmacologic agent that binds to a specific receptor and activates it, producing a biological effect similar to the body's natural ligand. Agonists contrast with antagonists, which bind to receptors but block activation.

Types of Agonists

• Full agonist: Produces maximal receptor response (morphine at mu opioid receptors).
• Partial agonist: Produces a less-than-maximal response (buprenorphine).
• Inverse agonist: Binds and produces the opposite effect of the natural ligand.

Clinical Examples

Albuterol (beta-2 adrenergic agonist for bronchodilation), morphine (opioid receptor agonist), insulin (insulin receptor agonist), dopamine agonists (Parkinson disease).

Nursing Considerations

Understand the receptor mechanism to anticipate both therapeutic effects and side effects. Beta-2 agonists cause tachycardia and tremor; opioid agonists cause respiratory depression and constipation. Monitor closely during initial doses and dose escalations.

NCLEX Relevance

Foundational pharmacology concept needed to reason about drug classes, often paired with antagonist questions (naloxone reverses opioid agonists).