Okay, let's tackle this question about the drug used for both treatment and prophylaxis of angina pectoris. First, I need to recall the main classes of drugs used for angina. The primary ones are nitrates, beta-blockers, calcium channel blockers, and sometimes ranolazine.

The question is asking for a drug effective in both treating acute episodes and preventing them. Nitrates like nitroglycerin are typically for acute relief, but they might not be the best for long-term use. Beta-blockers like propranolol are used for both acute and long-term management because they reduce heart rate and myocardial oxygen demand. Calcium channel blockers such as amlodipine can also be used for both, especially in certain types of angina like variant angina.

Wait, the correct answer is probably a beta-blocker. They are known for both acute and chronic use. Let me confirm: beta-blockers work by blocking beta-adrenergic receptors, decreasing heart rate, contractility, and blood pressure, which reduces the heart's oxygen demand. For prophylaxis, they're taken daily. For acute treatment, they can be administered intravenously or via sublingual routes. So a drug like metoprolol would fit here.

Looking at the options, if one of them is a beta-blocker, that's the correct answer. The other options might include nitrates which are more for acute use, or calcium channel blockers which might be more for specific types. Also, ranolazine is newer and used more for chronic management. So the correct answer is likely the beta-blocker.

**Core Concept**
Angina pectoris is managed by reducing myocardial oxygen demand and improving supply. **Beta-blockers** are first-line for both acute treatment and long-term prophylaxis due to their ability to decrease heart rate, contractility, and blood pressure.

**Why the Correct Answer is Right**
**Beta-blockers** (e.g., metoprolol, atenolol) inhibit β1-adrenergic receptors in the heart, reducing myocardial oxygen consumption. They are administered sublingually for acute angina and orally for chronic prophylaxis. By decreasing heart rate and blood pressure, they alleviate ischemic chest pain and prevent recurrent episodes.

**Why Each Wrong Option is Incorrect**
**Option A:** Nitrates (e.g., nitroglycerin) are effective for acute angina but lack long-term prophylactic efficacy. They dilate coronary vessels but may cause tolerance with chronic use.
**Option B:** Calcium channel blockers (e.g., verapamil) are used for variant angina and chronic management but are less effective in acute settings compared to beta-blockers.
**Option D:** Ranolazine is a late addition for chronic angina and does not address acute episodes.

**Clinical Pearl**
Beta-blockers are the **gold standard** for both acute and chronic angina. Avoid them in patients with asthma or severe bradycardia. Always prescribe the lowest effective dose to minimize adverse effects like hypotension or fatigue.

**Correct Answer: B. Beta-blockers**

✓ Correct Answer: A. Isosorbide dinitrate