Mepyramine
Mepyramine
First generation antihistamine
Mepyramine, also known as pyrilamine, is a first generation antihistamine, targeting the H1 receptor as an inverse agonist.[1] Mepyramine rapidly permeates the brain, often causing drowsiness.[2] It is often sold as a maleate salt, pyrilamine maleate.
The medication has negligible anticholinergic activity, with 130,000-fold selectivity for the histamine H1 receptor over the muscarinic acetylcholine receptors (for comparison, diphenhydramine had 20-fold selectivity for the H1 receptor).[3]
It was patented in 1943 and came into medical use in 1949.[4] It was marketed under the names Histadyl, Histalon, Neo-Antergan, Neo-Pyramine, and Nisaval.[5] In the 1960s and 70s it was a very common component in over-the-counter sleep aids such as Alva-Tranquil, Dormin, Sedacaps, Sominex, Nytol, and many others.[5] The US FDA included it in the list of chemicals and compounds barred from use in over-the-counter nighttime sleep aid products in 1989.[6]
It is used in over-the-counter combination products to treat the common cold and menstrual symptoms such as Midol Complete.[7] It is also the active ingredient of the topical antihistamine creams Anthisan[8] and Neoantergan[1] sold for the treatment of insect bites, stings, and nettle rash.
