Final answer:
N-acetylcysteine (Choice A) is the most likely pharmacologic therapy to be protective against acute kidney injury in the described patient.
Step-by-step explanation:
The pharmacologic therapy most likely to be protective against acute kidney injury in a patient undergoing mitral valve repair, who has a history of hypertension, diabetes mellitus type 2, and mild chronic renal insufficiency, is N-acetylcysteine (Choice A). N-acetylcysteine is an antioxidant that can help to protect the kidneys from the contrast-induced nephropathy (CIN) during procedures that require contrast agents. Although diuretics like mannitol (Choice D) and furosemide (Choice E) are sometimes used in certain acute kidney injury cases, they are not considered protective in this clinical scenario.
Fenoldopam (Choice C) is a dopaminergic agonist and could theoretically protect kidney function by increasing renal blood flow, but it is not as widely recommended as N-acetylcysteine for protecting against acute kidney injury. Dopamine (Choice B) has fallen out of favor because clinical studies have not shown it to be effective at preventing or treating acute kidney injury in this context.