Pharmacy PEBC Practice Exam

Antihistamines primarily function by blocking histamine receptors, which helps alleviate the symptoms associated with allergic reactions. Histamine is a chemical released by the body during an allergic response, leading to various symptoms such as itching, sneezing, runny nose, and swelling. By inhibiting the action of histamine at its receptor sites, antihistamines prevent these symptoms from occurring or reduce their severity.

This mechanism of action is particularly beneficial in treating conditions like allergic rhinitis, hay fever, and urticaria. There are two main types of histamine receptors that are relevant here: H1 and H2 receptors. Most commonly, when discussing antihistamines, we are referring to H1 antagonists, which directly counteract the effects produced by histamine in allergic responses.

In contrast, the other answer choices do not represent the actions of antihistamines. Enhancing histamine production would exacerbate allergic symptoms, while stimulating the immune response would generally lead to increased inflammation and allergy symptoms as well. Lastly, antihistamines are not primarily designed to decrease blood pressure; while some antihistamines may have sedative effects that can influence overall cardiovascular responses, this is not their primary action.