Ondansetron

Pregnancy & gynaecology-specific. Every dose row is source-referenced; verify against institutional protocols.

Ondansetron5-HT3 antagonist

Guideline conflict

MSF injectable ondansetron monograph
General postoperative-vomiting reference advises avoiding first-trimester use and does not recommend it for nausea/vomiting of pregnancy.

RCOG Green-top 69, 2024
Includes ondansetron as a second-line HG treatment with counselling about the small absolute fetal-risk signal and the harms of inadequately treated HG.

Population/setting difference: A general injectable/postoperative reference and a specialist pregnancy/HG pathway address different indications and prescribing decisions.

Practical India consideration: Review first-line response, gestation, electrolyte/QT risk and available routes with the patient and treating obstetric team.

App default: Use the RCOG HG-specific second-line schedules after assessment and counselling; do not import the postoperative injection schedule.
Reason: The specialist pregnancy pathway directly addresses HG, its competing risks and route-specific dosing.

Regimens checked: 2026-10-17. Each indication has its own preparation, limits and safety checks.

Ondansetron: indication-specific regimens
Indication	Dose	Route	Frequency	Duration / preparation	Maximum	Monitoring / cautions
Second-line nausea/vomiting or hyperemesis after assessment and discussion of benefits and small absolute fetal-risk signals RCOG / BJOGchecked	4 mg every 8 h OR 8 mg every 12 h	Oral	Use ONE of these schedules	Review daily during acute illness; reduce/stop as oral intake and symptoms improve rather than prescribe a fixed long course · Use the prescribed tablet/orodispersible formulation; correct dehydration and electrolyte disturbance This obstetric guideline differs from the more restrictive MSF general ondansetron monograph; the app uses the RCOG HG pathway after counselling.	12 mg/day for 4 mg every 8 h OR 16 mg/day for 8 mg every 12 h; severe hepatic impairment max 8 mg/day	Monitor Response, constipation, QT/ECG risk, potassium/magnesium and interacting QT-prolonging drugs Contraindications / cautions Congenital long QT or significant electrolyte derangement needs correction/specialist review
Second-line HG when oral treatment cannot be retained RCOG / BJOGchecked	8 mg over 15 min	IV infusion	Every 12 hours	Review daily; change to oral treatment when tolerated · 2 mg/mL solution: 8 mg = 4 mL; dilute in compatible IV fluid according to the actual product label and infuse over 15 min, not rapid IV push	16 mg/day in this RCOG HG regimen; severe hepatic impairment max 8 mg/day	Monitor ECG/QT risk, potassium/magnesium, symptom control and constipation Contraindications / cautions Correct significant electrolyte disturbance; review other QT-prolonging drugs

Pregnancy safety

RCOG second-line HG option after counselling; correct electrolytes and evaluate QT risk.

Lactation

Compatible

RCOG / BJOGcheckedIN REVIEW