Mepyramine, also known as pyrilamine, is a

first generation antihistamine H1 antagonists, also called H1 blockers, are a class of medications that block the action of histamine at the H1 receptor, helping to relieve allergic reactions. Agents where the main therapeutic effect is mediated by negative modulation of ...

, targeting the H₁ receptor as an

inverse agonist In pharmacology, an inverse agonist is a drug that binds to the same receptor as an agonist but induces a pharmacological response opposite to that of the agonist. A neutral antagonist has no activity in the absence of an agonist or inverse ago ...

. Mepyramine rapidly permeates the brain, often causing

drowsiness Somnolence (alternatively sleepiness or drowsiness) is a state of strong desire for sleep, or sleeping for unusually long periods (compare hypersomnia). It has distinct meanings and causes. It can refer to the usual state preceding falling asleep ...

. It is often sold as a

maleate Maleic acid or ''cis''-butenedioic acid is an organic compound that is a dicarboxylic acid, a molecule with two carboxyl groups. Its chemical formula is HO2CCH=CHCO2H. Maleic acid is the ''cis''-isomer of butenedioic acid, whereas fumaric acid ...

salt, pyrilamine maleate. The medication has negligible

anticholinergic Anticholinergics (anticholinergic agents) are substances that block the action of the neurotransmitter called acetylcholine (ACh) at synapses in the central and peripheral nervous system. These agents inhibit the parasympathetic nervous sys ...

activity, with 130,000-fold selectivity for the

histamine Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Since histamine was discover ...

H₁ receptor over the

muscarinic acetylcholine receptor Muscarinic acetylcholine receptors, or mAChRs, are acetylcholine receptors that form G protein-coupled receptor complexes in the cell membranes of certain neurons and other cells. They play several roles, including acting as the main end- ...

s (for comparison,

diphenhydramine Diphenhydramine (DPH) is an antihistamine and sedative mainly used to treat allergies, insomnia, and symptoms of the common cold. It is also less commonly used for tremor in parkinsonism, and nausea. It is taken by mouth, injected into ...

had 20-fold selectivity for the H₁ receptor). It was patented in 1943 and came into medical use in 1949. It was marketed under the names Histadyl, Histalon, Neo-Antergan, Neo-Pyramine, and Nisaval. 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. It is used in over-the-counter combination products to treat the common cold and menstrual symptoms such as Midol Complete. It is also the active ingredient of the topical antihistamine creams ''Anthisan'' and ''Neoantergan'' sold for the treatment of insect bites, stings, and nettle rash.

References

Aminopyridines H1 receptor antagonists Muscarinic antagonists Phenol ethers Sigma receptor ligands {{dermatologic-drug-stub

See also

References