How should I manage acute vomiting?

Management of Acute Vomiting

For acute vomiting, start with ondansetron 8 mg (sublingual or oral) every 4-6 hours as your first-line antiemetic, ensure adequate hydration with oral or intravenous fluids, and resume eating small frequent meals as soon as tolerated. 1, 2

Immediate Assessment and Risk Stratification

Before treating, quickly determine:

• Severity: Number of episodes in 24 hours (mild: 1-2 episodes; moderate: 3-5 episodes; severe: ≥6 episodes) 3
• Hydration status: Check for signs of dehydration (dry mucous membranes, decreased urine output, orthostatic changes)
• Red flags requiring urgent evaluation: Severe abdominal pain, blood in vomit, neurologic symptoms, suspected obstruction, or pregnancy 1

First-Line Pharmacologic Treatment

Ondansetron is the preferred first-line agent for acute vomiting across multiple clinical contexts 1, 2, 3:

• Dose: 8 mg sublingual or oral every 4-6 hours
• Advantages: Highly effective 5-HT3 receptor antagonist, well-tolerated, available in dissolving tablets for patients actively vomiting
• Caution: Obtain baseline ECG if available, as ondansetron can prolong QTc interval 1

Alternative and Second-Line Antiemetics

If ondansetron fails or is contraindicated, use these agents sequentially:

Prochlorperazine (dopamine antagonist) 1, 3:

• 5-10 mg oral every 6-8 hours, OR
• 25 mg suppository every 12 hours
• Watch for: Extrapyramidal symptoms, CNS depression
• Avoid in: Dementia, glaucoma, seizure disorders

Promethazine (antihistaminergic/anticholinergic) 1:

• 12.5-25 mg oral or rectal every 4-6 hours
• Critical warning: If given IV, must use central line only—peripheral administration causes tissue injury including gangrene

Metoclopramide (dopamine antagonist/prokinetic) 3, 4:

• 10-20 mg oral or IV every 4-6 hours
• Useful when gastroparesis suspected
• Monitor for dystonic reactions

Essential Supportive Care

Hydration is paramount 2:

• Mild vomiting: Oral rehydration with small, frequent sips of clear fluids
• Moderate-severe vomiting: IV fluids with electrolyte replacement (0.9% saline or dextrose-containing solutions) 5
• Check and correct electrolyte abnormalities, particularly in prolonged vomiting

Early refeeding improves outcomes 2:

• Resume small, frequent meals as soon as vomiting controlled
• No need to wait 24 hours before eating solid food
• Avoid trigger foods, but the BRAT diet has limited supporting evidence

When to Escalate Treatment

If first-line therapy fails, add agents from different drug classes 4:

For breakthrough vomiting:

• Lorazepam 0.5-2 mg every 4-6 hours (addresses anxiety component) 1, 4
• Diphenhydramine 12.5-25 mg every 4-6 hours (antihistamine) 1
• Haloperidol 0.5-2 mg every 4-6 hours (for refractory cases) 4

Consider hospitalization if:

• Unable to tolerate oral fluids
• Signs of severe dehydration
• Persistent vomiting despite appropriate antiemetics
• Underlying serious condition suspected

Special Considerations and Pitfalls

Cannabis use: If patient uses cannabis regularly (>4 times weekly), consider cannabinoid hyperemesis syndrome—hot showers provide temporary relief, and cannabis cessation for 6 months is diagnostic and therapeutic 1

Pregnancy: Ondansetron may be used cautiously; avoid promethazine in first trimester; metoclopramide is generally safe 1

Elderly patients: Use lower doses of all antiemetics; avoid diphenhydramine due to anticholinergic effects and confusion risk 1

Drug interactions: If patient on QTc-prolonging medications, choose prochlorperazine or promethazine over ondansetron 1

Treatment Duration

Use antiemetics for the shortest time necessary 6:

• Acute viral gastroenteritis: Typically 24-48 hours
• Continue until vomiting controlled and patient tolerating oral intake
• Avoid chronic daily use without identifying underlying cause

When Symptoms Persist Beyond 7 Days

If vomiting continues >7 days, this becomes chronic and requires diagnostic evaluation 6, 7:

• Basic labs: CBC, electrolytes, glucose, liver function, lipase
• Consider upper GI imaging or endoscopy to exclude obstruction
• Evaluate for metabolic causes (Addison's disease, hypothyroidism, porphyria)
• Neurologic evaluation if any focal symptoms present 1