Ondansetron

• Hyperemesis gravidarum unresponsive to 1st-line antiemetics

Blocks central & peripheral 5-HT3 receptors in CTZ and gut → ↓ vomiting reflex.

• Avoid before 10 weeks if possible (cleft palate signal, NNH ~1/1000)
• OK after 10 weeks
• Watch QT — avoid with other QT-prolonging drugs

Oral / IV

4–8 mg q8h

Max

16 mg/day (QT risk above)

• AbsoluteCongenital long QT
• CautionCombine with apomorphine — hypotension

• Constipation, headache
• QT prolongation
• Rare: serotonin syndrome with SSRIs

• • Small absolute ↑ risk of cleft palate (use after 10 wks ideally).
• • No ↑ in overall malformation rate.
• • Safe in breastfeeding.

• QT-prolonging drugs

  Avoid

  Additive QT — avoid

• SSRIs / SNRIs

  Caution

  Serotonin syndrome (rare)

• 💡 1st-line: cyclizine, promethazine, prochlorperazine.
• 💡 Always assess hydration, ketosis, weight loss in HG.