ANTIHISTAMINE ANTIEMETICS...
EXAMPLES: Cyclizine, promethazine.
MECHANISM OF ACTION: H1 receptor antagonists directly inhibit the CTZ in the medulla.
They possess anticholinergic and anti-emetic properties. Cyclizine also increases lower
oesophageal sphincter tone and reduces the sensitivity of the labyrinthine apparatus.
- Nausea and vomiting.
- Hyperemesis in pregnancy (promethazine is first line).
- Vomiting in labyrinthine disorders.
- Nausea associated with motion sickness.
- Severe prostatic hypertrophy.
- Caution in patients at risk of closed-angle glaucoma.
- Drowsiness.
- Headache.
- Tachycardia (cyclizine).
- Psychomotor impairment.
- Antimuscarinic effects.
- Metabolised by the liver to an inactive metabolite. t½ for cyclizine is ∼20 h.
- No specific drug monitoring required.
- Increased sedative effect with opiates.
- Establish a cause for emesis prior to prescribing an anti-emetic.
- Sedative effects of antihistamines are likely to be potentiated in liver disease.
- Cyclizine and promethazine are safe to prescribe in pregnancy.
Tags:
Pharmacology