Which medication is described as having the longest duration and a half-life of approximately 30 minutes?

The correct medication is Nicardipine, which is a calcium channel blocker commonly used in the management of hypertension and angina. It has a long duration of action due to its ability to maintain its therapeutic effects over an extended period, despite its relatively short half-life of approximately 30 minutes. This characteristic allows for effective management of blood pressure without constant dosing, making it suitable for intravenous administration in various clinical settings.

In contrast, nitroglycerin's duration can vary widely, often requiring more frequent dosing to maintain effect, as its action can depend significantly on the formulation and route of administration. Phenylephrine, while also having a longer duration when used at higher doses, does not compare to the sustained effects provided by Nicardipine in the context of blood pressure control. Vasopressin is a hormone with different pharmacokinetics, primarily used for its vasopressor effects, but it does not match the 30-minute half-life referenced in the question. Thus, Nicardipine stands out in this scenario for its appropriate duration of action correlating to its half-life.