Hyoscyamine

Hyoscyamine (also known as daturine) is a tropane alkaloid. It is a secondary metabolite found in certain plants of the Solanaceae family, including henbane (Hyoscyamus niger), mandrake (Mandragora officinarum), jimsonweed (Datura stramonium), tomato (Solanum lycopersicum) and deadly nightshade (Atropa belladonna). It is the levorotary isomer of atropine (third of the three major nightshade alkaloids) and thus sometimes known as levo-atropine. Hyoscyamine should not be confused with hyoscine, an older alternate name for the related nightshade-derived anticholinergic scopolamine for which it is the precursor.

Brand names for hyoscyamine include Symax, HyoMax, Anaspaz, Egazil, Buwecon, Cystospaz, Levsin, Levbid, Levsinex, Donnamar, NuLev, Spacol T/S and Neoquess.

Biosynthesis in plants
Hyoscyamine can be extracted from plants of the Solanaceae family, notably Datura stramonium. As hyoscyamine is a direct precursor in the plant biosynthesis of scopolamine, it is produced via the same metabolic pathway.

The biosynthesis of scopolamine begins with the decarboxylation of L-ornithine to putrescine by ornithine decarboxylase (EC 4.1.1.17). Putrescine is methylated to N-methylputrescine by putrescine N-methyltransferase (EC 2.1.1.53).

A putrescine oxidase (EC 1.4.3.10) that specifically recognizes methylated purtrescine catalizes the deamination of this compound to 4-methylaminobutanal which then undergoes a spontaneous ring formation to N-Methyl-pyrrolium cation. In the next step, the pyrrolium cation condenses with acetoacetic acid yielding hygrine. No enzmyatic activity could be demonstrated that catalyzes this reaction. Hygrine further rearranges to tropinone.

Subsequently, Tropinone reductase I (EC 1.1.1.206) converts tropinone to tropine which condenses with phenylalanine-derived phenyllactate to littorine. A cytochrome P450 classified as Cyp80F1 oxidizes and rearranges littorine to hyoscyamine aldehyde.

Uses
Hyoscyamine is used to provide symptomatic relief to various gastrointestinal disorders including spasms, peptic ulcers, irritable bowel syndrome, diverticulitis, pancreatitis, colic and 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 respiratory secretions in palliative care. It may be useful in pain control for neuropathic pain treated with opioids as it increases the level of analgesia obtained. Several mechanisms are thought to contribute to this effect. The closely related drugs atropine and scopolamine 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.

Side effects
Side effects include dry mouth and throat, eye pain, blurred vision, restlessness, dizziness, arrhythmia, flushing, and faintness. An overdose will cause headache, nausea, vomiting, and central nervous system symptoms including disorientation, hallucinations, euphoria, sexual arousal, short-term memory loss, and possible coma in extreme cases. The euphoric and sexual effects are stronger than those of atropine but weaker than those of scopolamine, as well as dicycloverine, orphenadrine, cyclobenzaprine, trihexyphenidyl, and ethanolamine antihistamines like phenyltoloxamine.

Hallucinogenic use
Hyoscyamine was one of the active principles in many of the "flying ointments" used to obtain flying sensations sought by users of these compounds. Potions, solids of various types, and other forms were used. These ointments could contain any number of ingredients with belladonna, henbane, and other plants of the belladonna and datura families being present almost invariably; they were applied to large areas of the skin with the objective being to see the gods/spirits or to be transported to the Sabbat.

The hallucinations, sensation of flying, often a rapid increase in libido, and other characteristic effects of this compound are largely attributable to the CNS and peripheral effects of hyoscyamine and other active drugs present in the ointments such as atropine, scopolamine, and other tropane alkaloids.

The inclusion of belladonna/datura type plants among the dozens of ingredients in the Haitian zombie drug is thought by some authorities to be at least somewhat likely, although scopolamine-bearing plant matter is almost certainly not the main active ingredient, which has been theorised to possibly be tetrodotoxin or a related substance.

Pharmacology
Hyoscyamine is an anticholinergic, specifically an antimuscarinic, working by blocking the action of acetylcholine at parasympathetic sites in smooth muscle, secretory glands and the CNS. It also increases cardiac output, dries secretions, and antagonizes serotonin. At comparable doses, hyoscyamine has 98 per cent of the anticholinergic power of atropine. The other major belladonna-derived drug scopolamine has 92 per cent of the antimuscarinic potency of atropine.