Final answer:
The antihistamine used to treat allergic reactions from the options provided is Diphenhydramine (Benadryl). It helps reduce symptoms like sneezing, itching, and runny nose by blocking H₁-histamine receptors in the body.
Step-by-step explanation:
An antihistamine used in the treatment of allergic reactions is D. Diphenhydramine (Benadryl). Antihistamines are medications that counteract the effect of the natural chemical histamine in the body, which is responsible for symptoms of allergies, such as sneezing, itching, and runny nose. Diphenhydramine (Benadryl) is commonly used as it binds to and blocks the H₁-histamine receptors, which are found in our mast cells as well as in smooth muscle and the brain. This action helps alleviate the symptoms associated with allergic reactions.
Antihistamines come in different forms and can be classified into two main categories: H₁-antihistamines and H₂-antihistamines. The former, which includes diphenhydramine, primarily targets symptoms experienced in the nose (such as a runny nose and sneezing) and may also be used to treat other conditions such as insomnia and motion sickness. The latter are used to treat gastric acid conditions. When dealing with more severe allergic reactions, such as anaphylaxis, emergency treatments like epinephrine are required.