Final answer:
The most indicated pharmacologic agent in this case is lopressor.
Step-by-step explanation:
The pharmacologic agent that is most indicated in a patient who has been intubated for several weeks, becomes tachypneic and tachycardic during every attempt to wean from the ventilator is C) lopressor. Lopressor, also known as metoprolol, is a beta-blocker that can be used to manage tachycardia and hypertension. It works by blocking the effects of adrenaline on the beta receptors in the heart, reducing heart rate and blood pressure.