C18H21N3O3S

C18H21N3O3S is a chemical compound with the systematic name *N*-(4-hydroxyphenyl)acetamide-*N*-(2-methylpropyl)-*N*-(2-pyridinylmethyl)ethanamine-2-sulfonamide, commonly recognized as **mepyramine maleate**, a widely used antihistamine. It belongs to the class of ethylenediamine derivatives and is primarily employed in the treatment of allergic reactions, including hay fever, hives, and other hypersensitivity responses.

Mepyramine maleate acts by selectively blocking histamine H1 receptors, thereby reducing symptoms such as itching, sneezing, and nasal congestion. The compound was first synthesized in the early 20th century and remains a key pharmaceutical agent in both human and veterinary medicine. Its chemical structure features a sulfonamide group, which contributes to its pharmacological activity.

The molecular formula C18H21N3O3S indicates a relatively small organic molecule with a balanced combination of carbon, hydrogen, nitrogen, oxygen, and sulfur atoms. The presence of nitrogen and sulfur suggests potential interactions with biological receptors, enhancing its efficacy as an antihistamine. Mepyramine maleate is typically administered orally, though it may also be used topically in certain formulations.

While generally well-tolerated, mepyramine can cause side effects such as drowsiness, dry mouth, or gastrointestinal discomfort. Its use is contraindicated in individuals with known hypersensitivity to the compound or related ethylenediamine derivatives. The compound has been studied extensively for its pharmacological properties, contributing to advancements in allergy treatment and drug development.