Mepyramine – Wikipedia

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]

It is used in over-the-counter combination products to treat the common cold and menstrual symptoms such as Midol Complete.^[6] It is also the active ingredient of the topical antihistamine creams Anthisan^[7] and Neoantergan^[1] sold for the treatment of insect bites, stings, and nettle rash.

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