Antihistamine anti-emetics

H1 receptor antagonists directly inhibit the CTZ in the medulla. They possess anticholinergic and anti-emetic properties....
Abdelwahab Ward, BS Pharm, PharmD
Antihistamine antiemetics...
  1. EXAMPLES: Cyclizine, promethazine.
  2. 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.
Accordion
  • 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.
Abdelwahab Ward, BS Pharm, PharmD