Nitroglycerin is contraindicated in patients:

• A. With a systolic blood pressure greater than 160 mm Hg.
• B. In patients who have taken a nitrate in the last 24 hours.
• C. With a systolic blood pressure less than 120 mm Hg.
• D. In patients with a heart rate over 120.

Answer: (C)

Nitroglycerin works by dilating blood vessels, which lowers preload and afterload and reduces the heart’s oxygen demand. The danger is that this vasodilation can cause a drop in blood pressure. If the systolic blood pressure is already low, giving nitroglycerin can push it down further and compromise perfusion to vital organs. That makes a low systolic BP the strongest reason to withhold nitroglycerin in this scenario, hence the best answer.

High blood pressure isn’t itself a contraindication to nitroglycerin and can be a situation where nitro is beneficial with careful monitoring. A heart rate over 120 isn’t an absolute stop sign for giving it. A recent nitrate use is a safety concern, but the immediate and direct risk of hypotension with a low BP is the primary reason to avoid it in this case.