Cyclizine

Question 1

What is cyclizine used to treat?

Answer 1

Nausea

Vomiting

Vertigo

Motion sickness

Labyrinthe disorders

Question 2

Describe the pharmacodynamics of cyclizine

Answer 2

A H1 recptor antagonist with anticholinergic properties

Vomiting (emesis) is controlled by the vomiting centre in the medulla of the brain. The neurons have muscarinic chollinergic and histamine synapses/receptors.

Cyclizine reduces activity of these neurons by blocking muscarinic and histamine receptors.

Question 3

Describe the pharmacokinetics of cyclizine

Answer 3

Half life = 20 hours

Metabolised to N-demethylated derivative - norcyclizine which has little antihistaminic activity in comparison to cyclizine

Question 4

What are the contraindications for cyclizine?

Answer 4

Do not use in neonates because of it antimuscarinic activity

Avoid using in pregnancy

Question 5

What are most clinically significant (common and/or potentially life threatening) side effects of the drug?

Answer 5

Level of consciousness decreased (with oral use)

Injection site necrosis, thrombophlebitis (with parenteral use)

Dry mouth

Abdominal pain

Leucopenia/agranulocytosis

Question 6

Is any monitoring required?

Answer 6

Use with caution in hepatic impairment

Question 7

What are the most clinically significant drug interactions?

Answer 7

Isocarboxazid + Cyclizine = increased risk antimuscarinic adverse effects

Phenylzine + Cyclizine = increased risk antimuscarinic adverse effects

Tranylcypromine + Cyclizine = increased risk antimuscarinic adverse effects