A nurse administered nitroglycerin sublingually to client who has angina pectoris and experienced chest pain. The client states that his chest pain is relieved but now he has a headache. Which of the following responses by the nurse is appropriate?

A) A headache indicates tolerance to the medication:
A headache does not indicate tolerance to nitroglycerin. Tolerance typically refers to the need for increasing doses to achieve the same therapeutic effect, which is more common with medications like nitroglycerin when used chronically. 

B) It sounds as if you are allergic to this medication:
While headaches are a common side effect of nitroglycerin, they are not an allergic reaction. Allergies typically cause symptoms such as rash, itching, or swelling, and are not typically associated with nitroglycerin use. Therefore, attributing the headache to an allergy would be inappropriate.

C) Your headache is probably a result of anxiety about the chest pain:
While anxiety can contribute to physical symptoms like headaches, it is not the most likely cause in this case. Nitroglycerin causes vasodilation, which can lead to headaches as a common side effect. Given that the headache occurred shortly after taking the medication, it is much more likely that the headache is a direct result of the nitroglycerin rather than anxiety about the chest pain.

D) A headache is a common adverse effect of this medication, but it will probably occur less often over time:
Headaches are a well-known and common side effect of nitroglycerin due to its vasodilatory effect, which can cause blood vessels in the head to expand, leading to a headache. The nurse's response is appropriate because it reassures the client that the headache is a typical reaction and that it often becomes less frequent with continued use. The nurse should also remind the client to take the medication as prescribed, and if the headache persists or worsens, they should notify their healthcare provider.