Beta Blockers USMLE Step 1 Practice Question

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?