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Anticholinergics

Created: 2/4/2004
 

Hyoscine

Structure


The structure of hyoscine

Uses

In premedication, in the prophylaxis of motion sickness and as an antispasmodic.

Chemical

An alkaloid derived from Scopolia carniolica. It is an ester of tropic acid and scopine. It is a racemic mixture ( L- form is active).

Presentation

Clear solution for injection containing 0.4 mg/ml. Hyoscine butylbromide is a clear solution containing 20 mg/ml and it is also available in 10 mg tablet form. Also presented as a transdermal patch delivering 0.5 mg.

Mode of action

Competitive antagonism of acetylcholine at muscarinic receptors. When administered together with an IM opioid, hyoscine has been shown to reduce postoperative nausea and vomiting. Hyoscine also decreases muscle tone and secretions in the gut, which may contribute to its antiemetic properties.

Dose

May be administered IM, IV, SC, transdermally or orally. IM dose is 0.008 mg/kg. Oral dose in adults is 20 mg 6-hourly.

Effects

CVS: 
IV administration may cause an initial tachycardia followed by a bradycardia.

Respiratory:
Decrease in bronchial secretions, mild bronchodilatation and stimulation of respiration.

Gastrointestinal:
Anti-spasmodic and anti-sialogogue.

Toxicity:
Central anticholinergic syndrome (caution in elderly). Hyoscine may precipitate porphyria in susceptible patients.

Absorption:
Poor oral absorption. 10% bioavailability. Well absorbed by SC or IM route.

Distribution:
11% protein bound. Volume of distribution 2 L/kg.

Metabolism:
Hepatic metabolism to scopine and scopic acid.

Excretion:
2% excreted unchanged in the urine, 5% in the bile. Clearance is 45 L/hour. Elimination half life is 2.5 hours.

References

[i] The efficacy and safety of transdermal scopolamine for the prevention of postoperative nausea and vomiting: a quantitative systematic review.
Kranke P et al.
Anesth Analg 2002; 95(1): 133-43.

[ii] Prevention of postoperative nausea and vomiting with transdermal hyoscine in children using patient-controlled analgesia.
Doyle E et al.
Br J Anaesth 1994; 72(1): 72-6.


ArticleDate:20040402
SiteSection: Article
 
   
    
                                            
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