Commonly used to manage nausea and vomiting from a range of causes, particularly useful in vestibular disorders.
Contraindications
Caution
Patients at risk of:
- Bladder outflow obstruction and urinary retention
- Acute angle closure glaucoma
- Pyloro-duodenal obstruction
And in:
- Severe hepatic failure, the sedative action added to hepatic encephalopathy may precipitate a coma
- Children
- Elderly
- Patients with epilepsy
- Severe heart failure
In addition, cyclizine may counter-act the beneficial haemodynamic effects of morphine in myocardial infarction and heart failure, so may be a suboptimal choice of anti-emetic in these situations.
Two sites in the brainstem are involved in vomiting: the chemoreceptor trigger zone (CTZ) and the vomiting centre. The CTZ responds to substances in the systemic circulation and the vomiting centre to neural input from the vestibular system, gut and other parts of the brain.
Anti-histamines block histamine receptors found mainly in the vestibular system and the vomiting centre, as well as muscarinic anti-cholinergic receptors in the vomiting centre. As they affect the vomiting centre (which is the common pathway for vomiting), these drugs are useful across a range of disease.
Available IV and orally, although in vomiting the IV route may be preferable. Can also be given by IM injection.
Drowsiness is a common side effect of cyclizine.
Anticholinergic side effects:
- Dilated pupils
- Blurred vision
- Dry mouth
- Nausea
- Constipation
- Headache
- Urinary retention / difficulty micturating
- Hypotension
- Psychomotor impairment
This combination of adverse effects may make antihistamines particularly problematic in the elderly, who are more susceptible to them (as are children).
Antihistamines potentiate the effects of other CNS depressants, including alcohol, benzodiazepines, phenothiazines.
Patients should be advised that drowsiness may occur and may affect performance tasks, for example driving.
Patients should be warned that excess alcohol should be avoided.
No specific issues.
Respiratory: Antihistamines
Available IM, IV and orally, although in vomiting the IV route may be preferable. Can also be given by subcutaneous infusion for nausea and vomiting associated with palliative care.
