A putrescine oxidase (EC 188.8.131.52) that specifically recognizes methylated putrescine catalyzes 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.
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 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.
^Edwards Pharmaceuticals, Inc.; Belcher Pharmaceuticals, Inc. (May 2010), DailyMed, U.S. National Library of Medicine, retrieved January 13, 2013
^Li, R.; Reed, D. W.; Liu, E.; Nowak, J.; Pelcher, L. E.; Page, J. E.; Covello, P. S. (2006). "Functional Genomic Analysis of Alkaloid Biosynthesis in Hyoscyamus niger Reveals a Cytochrome P450 Involved in Littorine Rearrangement". Chemistry & Biology13 (5): 513–520. doi:10.1016/j.chembiol.2006.03.005. PMID16720272.