Hyoscyamine

Action and Spectrum

Antagonizing muscarinic M1, M4, M5 receptors causes cognitive issues, while M2 antagonism increases heart rate and atrial contractility. 

Hyoscyamine requires multiple daily doses patients should be informed about anticholinergic toxicity risks and symptoms to monitor. 

Drug Interaction

Adverse Reaction

Adverse drug reactions:   

Frequency defined 

>10%  

Dry skin  

1-10%  

Dysphagia  

Photosensitivity  

Blurred vision  

Constipation  

<1%  

Orthostatic hypotension  

Headache  

Tachycardia  

Frequency Not Defined  

Dysphagia  

Respiratory depression  

CNS stimulation  

Xerostomia  

Urinary hesitancy  

HTN  

Palpitations  

Mydriasis  

Cycloplegia  

Fever  

Ataxia  

Excitation  

Lethargy  

Black Box Warning

None 

Contraindication / Caution

Contraindication: 

Hypersensitivity 

Closed-angle glaucoma 

Myasthenia gravis 

Paralytic ileus 

Caution: 

Discontinue treatment if diarrhea occurs 

May cause drowsiness 

Caution patients about performing a hazardous task, like driving heavy machinery 

Use caution in hot weather or exercise 

Pregnancy / Lactation

Pregnancy warnings:     

Pregnancy category: C. 

Breastfeeding warnings:  

The release of the drug into the human breastmilk is known 

Pregnancy Categories:      

Category A: Satisfactory and well-controlled studies show no risk to the fetus in the first or later trimester.      

Category B: No evidence shown of risk to the fetus found in animal reproduction studies, and there are not enough studies on pregnant women      

Category C: Adverse effects on the fetus found with evidence in animal reproduction studies and no adequate evidence for a result in humans must take care of potential risks in pregnant women      

Category D: There is adequate data available with sufficient evidence of human fetal risk from various platforms, but despite the potential risk, and used only in emergency cases for potential benefits      

Category X: Drugs listed in this category outweigh risks over benefits. Hence these categories of drugs need to be avoided by pregnant women.      

Category N: There is no data available for the drug under this category  

Pharmacology

Blocks acetylcholine action at muscarinic receptors in parasympathetic system. 

Relaxation of iris muscles causes dilation and may paralyze ciliary muscle affects accommodation. 

It increases heart rate to inhibit vagal input to the sinoatrial and atrioventricular nodes. 

Pharmacodynamics 

It reduces smooth muscle tone and peristalsis to alleviate cramps and spasms. 

M1 receptors found in the CNS to decreased gastric acid secretion. 

M3 receptors found in smooth muscle and exocrine glands to reduce glandular secretions. 

It relaxes detrusor muscles and contracts the internal sphincter to reduce urinary urgency and frequency. 

Pharmacokinetics 

Absorption: 

It has bioavailability of 100% for tablets and for sustained release of 81%. 

It has onset action through IV/IM/SC is 2 to 3 minutes and for tab/SR is 20 to 30 minutes. 

Peak plasma time reaches within 2.5 hours. 

Distribution: 

Volume of distribution: 1.2-1.9 L/kg.  

It has high protein binding up to 50%. 

Metabolism: 

It is metabolized through hepatic pathways. 

Elimination and excretion:  

It is excreted though urinary route 

Half-life for tablets is 3.5 hours and for SR is 5 to 9 hours. 

Adminstartion

It is available in tablet form for oral administration. 

Swallow whole tablet with water and never crush or chew the tablet. 

It is also available in form of elixir and oral drops. 

Patient Information Leaflet

Patient Information Leaflet 

Generic Name: hyoscyamine 

Pronunciation: hye-oh-SYE-a-meen 

Why do we use hyoscyamine? 

Hyoscyamine is used in treatment of GIT disorders. 

Intravenous hyoscyamine is indicated to reduce mouth and respiratory secretions for intubation. 

Oral hyoscyamine used to treat functional intestinal disorders.