indication

For treatment of bladder spasms, peptic ulcer disease, diverticulitis, colic, irritable bowel syndrome, cystitis, and pancreatitis. Also used to treat certain heart conditions, to control the symptoms of Parkinson's disease and rhinitis.

pharmacology

L-Hyoscyamine, the active optical isomer of atropine (dl-hyoscyamine), is a tertiary amine anticholinergic gastrointestinal agent.

mechanism of action

Hyoscyamine competes favorably with acetylcholine for binding at muscarinic receptors in the salivary, bronchial, and sweat glands as well as in the eye, heart, and gastrointestinal tract. The actions of hyoscyamine result in a reduction in salivary, bronchial, gastric and sweat gland secretions, mydriasis, cycloplegia, change in heart rate, contraction of the bladder detrusor muscle and of the gastrointestinal smooth muscle, and decreased gastrointestinal motility.

toxicity

Symptoms of overdose include headache, nausea, vomiting, blurred vision, dilated pupils, hot dry skin, dizziness, dryness of the mouth, difficulty in swallowing, and CNS stimulation. LD₅₀=mg/kg(orally in rat)

biotransformation

Hepatic

absorption

Absorbed totally and completely by sublingual administration as well as oral administration.

half life

2-3.5 hours

drug interactions

Donepezil: Possible antagonism of action

Galantamine: Possible antagonism of action

Haloperidol: The anticholinergic increases the risk of psychosis and tardive dyskinesia

Rivastigmine: Possible antagonism of action

Tacrine: The therapeutic effects of the central acetylcholinesterase inhibitor, Tacrine, and/or the anticholinergic, Hyoscyamine, may be reduced due to antagonism. The interaction may be beneficial when the anticholinergic action is a side effect. Monitor for decreased efficacy of both agents.

Trimethobenzamide: Trimethobenzamide and Hyoscyamine, two anticholinergics, may cause additive anticholinergic effects and enhance their adverse/toxic effects. Monitor for enhanced anticholinergic effects.

Triprolidine: Triprolidine and Hyoscyamine, two anticholinergics, may cause additive anticholinergic effects and enhance their adverse/toxic effects. Monitor for enhanced anticholinergic effects.

Trospium: Trospium and Hyoscyamine, two anticholinergics, may cause additive anticholinergic effects and enhanced adverse/toxic effects. Monitor for enhanced anticholinergic effects.