GI: ANTIEMETICS HISTAMINE H1-RECEPTOR ANTAGONISTS

Question 1

HISTAMINE H1-RECEPTOR ANTAGONISTS: INDICATIONS

Answer 1

• Prophylaxis for Nausea and Vomiting - in the context of motion sickness or vertigo

Question 2

HISTAMINE H1-RECEPTOR ANTAGONISTS: MOA

Answer 2

• HISTAMINE + ACH (muscarinic) receptors predominate in the vomiting centre and in its communication with the vestibular system
• Drugs such as Cyclizine block both of these receptors

Question 3

HISTAMINE H1-RECEPTOR ANTAGONISTS: ADVERSE EFFECTS

Answer 3

• Drowsiness
• Dry throat and mouth (anticholinergic effect)
• Transient tachycardia (following IV injection) -> patients can notice these as palpatations

Question 4

HISTAMINE H1-RECEPTOR ANTAGONISTS: CONTRA INDICATIONS

Answer 4

• Hepatic encephalopathy patients

- Prostatic hypertrophy patients = can cause urinary retention (or patients susceptible to anticholinergic side effects)

Question 5

HISTAMINE H1-RECEPTOR ANTAGONISTS: INTERACTIONS

Answer 5

• Sedation may be greater when combined with other sedative drugs (eg benzodiasepines or opioids)
  Anticholinergic effects may be more pronounced in patients taking ipratropium or tiotropium

Question 6

HISTAMINE H1-RECEPTOR ANTAGONISTS: EXAMPLES

Answer 6

• Cyclizine
• Cinnarizine
• Promethazine