Question

Which one of the following is employed as antihistamine?
A) Omeprazole
B) Chloramphenicol
C) Diphenhydramine
D) Norethindrone

Answer 1

Hint: Antihistamine is the class of drug that acts antagonistically against the histamine and thus blocking its receptors. Histamine is basically responsible for causing allergic reactions within the body like sneezing, coughing, skin reactions and so on.

Complete answer:
Histamines is the organic nitrogenous compound involved in local immune responses and is involved in producing inflammatory responses against the allergen.
In the type I hypersensitivity reactions, allergic reaction is carried out due to the re-exposure to a specific antigen (called as allergen) takes place within the body. It is the immediate hypersensitivity which results in showing clinical signs like sneezing, itching, vomiting, coughing etc.
Antihistamines are the drug that blocks the receptors of histamines and thus reduces the clinical sign of the allergic response. It blocks the H(1) receptors by the mechanism of inverse agonists. Examples include cetirizine, chlorpheniramine, diphenhydramine, fexofenadine, loratadine etc.

The correct option is C i.e. diphenhydramine.

Additional Information: Omeprazole is the hydrogen pump blocker that is responsible for decreasing the amount of acid produced in the stomach. Thus it is used for the treatment of gastro-esophageal reflux disease (GERD) and other conditions caused by the excess acid present in the stomach.
Chloramphenicol is the class of antibiotics that are used as bacteriostatic antibiotics.
Norethindrone is the steroidal progesterone that is used in birth control pills, menopausal hormonal therapy and for the treatment of gynaecological disorders.

Note: Diphenhydramine is used to relieve from hay fever, allergy and the common cold. It induces sleepiness, poor coordination and an upset stomach as a side effect. It is also an anticholinergic drug and thus acts against acetylcholine activity. It acts as an antitussive thus used for the treatment of dry cough and it acts as a constituent in Benadryl.