A 45-year-old man with a history of hypertension and resting heart rate consistently above 90 beats per minute is enrolled in a phase 1 clinical trial evaluating a novel antihypertensive agent. At baseline, his blood pressure is 158/96 mmHg and his ECG shows sinus tachycardia. He receives a single dose of the investigational drug, which binds to an allosteric site on a receptor and prevents downstream signaling even when high concentrations of agonist are present. Subsequent dose-response studies demonstrate that the maximal response to the agonist is reduced, but the receptor's affinity for the agonist remains unchanged, and the rightward shift of the dose-response curve cannot be overcome by increasing agonist concentration. Which of the following best describes this investigational drug?

1. A)Physiologic antagonist
2. B)Full agonist
3. C)Partial agonist
4. D)Competitive antagonist
5. E)Noncompetitive antagonistGABARITO