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You are in Home >> Resources >> Clinical anaesthesia >> Nausea and vomiting


Anti-histamines

Created: 5/4/2004
 

[i] Cyclizine

Structure

The structure of Cyclizine

Uses:
In the treatment of nausea and vomiting due to opioids, general anaesthesia, radiotherapy and Meniere’s disease.

Chemical:
Piperazine derivative.

Presentation:
Tablets containing 50 mg. Clear colourless solution for injection containing 50 mg/ml.

Mode of action:
Competitive antagonism of histamine H1 receptors. Its antiemetic effect may be via blockade of central histamine (H1) and muscarinic receptors, and indeed by its anticholinergic properties. Antihistamines that do not cross the blood-brain barrier (e.g. terfenadine) have no anti-emetic properties.

Effects

CVS:
Mild anticholinergic activity produces tachycardia.

Respiratory:
Exerts anti-histaminergic effects.

CNS:
Mild sedative effect.

Gastrointestinal:
Increase in tone of lower oesophageal sphincter.

Toxicity:
Anticholinergic effects: dry mouth, blurred vision. IM/IV route may be painful due to acidic preparation.

Absorption:
Good oral absorption. 80% bioavailability.

Metabolism:
Possibly N-demethylation to norcyclizine.

Excretion:
Elimination half life is 10 hours.

The drug is available as a compound preparation with morphine (Cyclimorph).

References

[i] A randomized double-blinded comparison of metoclopramide, ondansetron and cyclizine in day-case laparoscopy.
Watts SA.
Anaesth Intensive Care 1996; 24(5): 546-51.

[ii] Randomized, placebo-controlled trial of combination antiemetic prophylaxis for day-case gynaecological laparoscopic surgery.
Ahmed AB et al.
Br J Anaesth 2000; 85(5): 678-82.


[ii] Promethazine

Structure

The structure of Promethazine

Uses:
In the prevention and treatment of nausea and vomiting, allergic reactions, pruritus and for sedation in children.

Chemical:
Phenothiazine.

Presentation:
Tablets (10/25 mg), an elixir (1 mg/ml) and a clear, colourless solution for injection (25 mg/ml).

Mode of action:
Reversible competitive antagonist at H1 histaminergic receptors. Some anticholinergic, antiserotonergic and antidopaminergic activity.

Dose:
Adult oral dose is 20-75 mg daily. IM/IVdose is 25-50 mg.

Effects

CVS:
Rapid IV bolus may cause hypotension.

Respiratory:
Bronchodilatation, reduction in respiratory tract secretions, antitussive.

CNS:
Potent sedative and anxiolytic effect. Slight antanalgesic effect.

Gastrointestinal:
Decrease in tone of lower oesophageal sphincter.

Toxicity:
Anticholinergic side-effects. High doses may produce extrapyramidal reactions. Usage may result in jaundice, photosensitivity and haemopoietic disturbances.

Absorption:
Rapid oral absorption. Prone to extensive first-pass metabolism.

Distribution:
93% protein bound. Volume of distribution 2.5 L/kg.

Metabolism:
Hepatic metabolism. Undergoes sulfoxidation and N-dealkylation.

Excretion:
2% excreted unchanged in the urine. Clearance is 1.4 L/min. Elimination half life is 10 hours. Not removed by haemodialysis.

Promethazine has been used for premedication in children, and cyclizine is commonly used as an antiemetic in the preoperative period.


ArticleDate:20040405
SiteSection: Article
 
   
    
                                            
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