Hyoscyamine (also known as daturine or duboisine) is a naturally occurring tropane alkaloid and plant toxin. It is a secondary metabolite found in certain plants of the family Solanaceae, including henbane, mandrake, angel's trumpets, jimsonweed, the sorcerers' tree, and deadly nightshade. It is the Levorotatory isomer of atropine.
In 2021, it was the 272nd most commonly prescribed medication in the United States, with more than 900,000 prescriptions.
Medical uses
Brand names for hyoscyamine include Symax, HyoMax, Anaspaz, Egazil, Buwecon, Cystospaz, Levsin, Levbid, Levsinex, Donnamar, NuLev, Spacol T/S, and Neoquess.
Hyoscyamine is used to provide symptomatic relief of spasms caused by various lower abdominal and bladder disorders including peptic ulcers, irritable bowel syndrome, diverticulitis, pancreatitis, colic, and interstitial cystitis. It has also been used to relieve some heart problems, control some of the symptoms of Parkinson's disease, as well as for control of abnormal respiratory symptoms and "hyper-mucus secretions" in patients with lung disease.
It is also useful in pain control for neuropathic pain, chronic pain and palliative care — "comfort care" — for those with intractable pain from treatment resistant, untreatable, and incurable diseases. Several mechanisms are thought to contribute to this effect. The closely related drugs atropine and hyoscine and other members of the anticholinergic drug group like cyclobenzaprine, trihexyphenidyl, and orphenadrine are also used for this purpose. When hyoscyamine is used along with opioids or other anti-peristaltic agents, measures to prevent constipation are especially important given the risk of paralytic ileus.
Adverse effects
Side effects include dry mouth and throat, increased appetite leading to weight gain, eye pain, blurred vision, restlessness, dizziness, arrhythmia, flushing, and faintness.
Pharmacology
Pharmacodynamics
Hyoscyamine is an antimuscarinic; i.e., an antagonist of muscarinic acetylcholine receptors. It blocks the action of acetylcholine at sweat glands (sympathetic) and at parasympathetic sites in salivary glands, stomach secretions, heart muscle, sinoatrial node, smooth muscle in the gastrointestinal tract, and the central nervous system. It increases cardiac output and heart rate, lowers blood pressure and dries secretions. It may antagonize serotonin. At comparable doses, hyoscyamine has 98 percent of the anticholinergic power of atropine; the other major Atropa belladonna-derived drug hyoscine (known in the United States as scopolamine) has 92 per cent of the antimuscarinic potency of atropine. This is in contrast to related antimuscarinics like atropine and scopolamine, which are non-selective antagonists of all five muscarinic acetylcholine receptors.
Biosynthesis in plants
class=skin-invert-image|thumb|Biochemistry of tropane class compounds. Hyoscyamine and [[scopolamine are present and labeled in the diagram.]]
Hyoscyamine can be extracted from plants of the family Solanaceae, notably Datura stramonium. As hyoscyamine is a direct precursor in the plant biosynthesis of hyoscine, it is produced via the same metabolic pathway.
A generic presentation<!--Since there is no mention of the organism/plant from which this pathway is derived.--> of the steps in the biosynthesis of hyoscine, adapted from the review of Ziegler and Facchini, is illustrated below.
Ethnopharmacology
A plant extract used "for catching fish, in ceremony to connect with the spiritual realm", and as a bush medicine, "in a sleeping potion and for a variety of other uses", was developed by Aboriginal peoples from the soft corkwood tree, Duboisia myoporoides, found "in South Eastern NSW <nowiki>[</nowiki>New South Wales<nowiki>]</nowiki> across to Northern Queensland, Australia"; modern studies have shown the Aboriginal medicine to contain the alkaloids hyoscyamine and scopolamine.
thumb|alt=Brown glass medicine bottle label reading, "Clap Mixture" and a list of its ingredients.|Ingredients of a "Clap Mixture" (medical formulation), putatively hyoscyamine-containing, "Clap" being a colloquial synonym for "the [[sexually transmitted infection, gonorrhea". Interpretation of the label by Wikipedia editors deduce the "Extr. H..." (label obscured, at end of the first text line under the title) to refer to the article title subject, hysoscyamine, here putatively as a natural product extracted from an unspecified plant. Other indicated ingredients are interpreted to be: "Sod. Cit.", sodium citrate; "Sod. Bic., sodium bicarbonate; "Chlorof.", chloroform; "Aq.", aqueous, hence, the deduction is that this is an extract of hyoscyamine formulated for treatment of "the clap," also containing sodium citrate and sodium bicarbonate, in a solution/mixture of chloroform and water.]]
Society and culture
German-Australian botanist Baron Sir Ferdinand Jacob Heinrich von Mueller, on finding that Aboriginal communities had used a soft corkwood tree (Duboisia myoporoides) extract as a medicine, including for seasickness, led an effort to export the natural product isolate from Australia, and to create a "mystery pill" that was used by the Allies in World War II, specifically, to prevent seasickness among soldiers ferried across the English Channel during the Invasion of Normandy.