Why must nitroglycerin be administered cautiously in certain patients?

Nitroglycerin is essential in treating angina and certain cardiac conditions due to its vasodilatory effects, which help relieve chest pain by improving blood flow to the heart. However, it must be administered cautiously, especially in certain patient populations, because it can lower blood pressure excessively. This occurs through the dilation of blood vessels, leading to a reduction in systemic vascular resistance. In susceptible patients, like those with existing hypotension or significant blood volume depletion, this effect can cause dangerously low blood pressure, resulting in dizziness, fainting, or shock.

Other options listed do not reflect the primary concerns associated with nitroglycerin use. The medication is not known to significantly affect blood sugar levels, does not usually cause a rapid increase in heart rate, and while allergic reactions are possible, they are not common enough to warrant such caution as excessive blood pressure lowering. Therefore, understanding the effects of nitroglycerin, particularly in relation to blood pressure regulation, is crucial for safe and effective patient care.