Cyclizine

Cyclizine is an antihistamine drug used to treat nausea, vomiting and dizziness associated with motion sickness, vertigo and post-operative following administration of general anaesthesia and opioids.

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Pharmacology

Cyclizine is a piperazine derivative with histamine H₁-receptor antagonist (antihistamine) activity. The precise mechanism of action in inhibiting the symptoms of motion sickness is not well understood. It may have effects directly on the labyrinthine apparatus and on the chemoreceptor trigger zone. Cyclizine exerts a central anticholinergic (antimuscarinic) action.

Contraindications

Its antimuscarinic action warrants caution in patients with prostatic hypertrophy, urinary retention, glaucoma. Liver disease exacerbates its sedative effects. It cannot be combined with diclofenac, for example in the same syringe or bag of fluids, as a crystallisation reaction occurs.

Side effects

Common (>10%) - Drowsiness, xerostomia (dry mouth)

Uncommon (1% to 10%) - Headache, psychomotor impairment, and antimuscarinic effects such as urinary retention, diplopia (blurred vision), dermatitis, and gastro-intestinal disturbances.

Rare - Hypersensitivity reactions (bronchospasm, angioedema, anaphylaxis, rashes and photosensitivity reactions), extrapyramidal effects, dizziness, confusion, depression, sleep disturbances, tremor, liver dysfunction.

Formulations

As cyclizine hydrochloride 50mg tablets and cyclizine lactate solution for intramuscular or intravenous injection (Brand names: Valoid® in UK and Marezine®, Marzine® and Emoquil® in US)).

Abuse

In the UK the drug was removed from the shelves as an OTC preparation in the mid 80s because of it's interaction with opiates. It served to increase the 'flash' of injected opiates. Since opiate users would regularly use high doses, the number of ER room admissions due to seizures became a notable public health risk. Even so, the drug remains available on the internet and pockets of abuse still exist in the UK.

References

• British National Formulary 53 2007

Lexi-Online drug database http://online.lexi.com/crlsql/servlet/crlonline