Cyclizine

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

Indications
Nausea, vomiting and dizziness associated with motion sickness, vertigo and post-operatively following administration of general anaesthesia and opioids. An off-label use is as an opioid/opiate potentiator.

The drug Diconal is a combination of cyclizine with the opioid dipipanone. Diconal has been discontinued in the US for its high abuse potential.

Contraindications
Its antimuscarinic action warrants caution in patients with prostatic hypertrophy, urinary retention, or glaucoma. Liver disease exacerbates its sedative effects.

Adverse effects
Common (over 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 and hallucinations

Formulations
As cyclizine hydrochloride 50 mg tablets and cyclizine lactate solution for intramuscular or intravenous injection (brand names: Valoid in UK and Marezine, Marzine and Emoquil in US). Cyclizine HCl 25 mg is marketed as Bonine for Kids in the US.

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.

History
Cyclizine was developed in the American division of pharmacy company Burroughs Wellcome (today GlaxoSmithKline) during a research involving many drugs of the antihistamine group. Cyclizine was quickly clinically found as a potent and long-acting antiemetic. Company named the substance – or more precisely cyclizine's hydrochloride form which it usually appears in – "marezine hydrochloride" and started to sell it in the United States under trade name Marezine. Selling was begun in France under trade name Marzine in 1965.

The substance received more credit when NASA chose it as a space antiemetic for the first occupied moon flight. Cyclizine then spread into many West countries as a common antiemetic. It's still an over-the-counter drug in many countries because it has been well tolerated, although it's not very much studied.

Recreational use
Some people using methadone recreationally combine cyclizine with their methadone dose, a combination that is known to produce strong psychoactive effects. It has also been used recreationally by teenagers for its anticholinergic effects to induce hallucinations.