Competitive Antagonist

A drug that reversibly binds to the same receptor site as the agonist, competing for occupancy without activating the receptor. Competitive antagonism produces a rightward shift of the agonist dose-response curve with no reduction in maximal efficacy, as sufficiently high agonist concentrations can fully overcome the blockade. The magnitude of shift is quantified by the Schild equation and the dose ratio.

Exemples

• Naloxone: competitive antagonist at mu-opioid receptors, reverses opioid overdose
• Atropine: competitive antagonist at muscarinic acetylcholine receptors
• Losartan: competitive antagonist at angiotensin II AT1 receptors