What is the best approach to manage nausea and vomiting in a healthy adult?

Management of Nausea and Vomiting in Healthy Adults

Start with a dopamine receptor antagonist (metoclopramide 10 mg PO three times daily or prochlorperazine 5-10 mg PO three to four times daily) as first-line therapy, and add ondansetron 8 mg PO twice daily if symptoms persist after initial treatment. 1, 2

Initial Assessment

Before initiating treatment, rapidly assess for conditions requiring immediate intervention:

• Rule out mechanical bowel obstruction - never use antiemetics if obstruction is suspected, as this masks progressive ileus and gastric distension 1, 2
• Check for medication-induced causes - review all current medications and recent additions, as drug adverse effects are among the most common reversible causes 1, 3
• Assess hydration status - obtain serum electrolytes, particularly potassium and magnesium, as prolonged vomiting causes hypokalemia, hypochloremia, and metabolic alkalosis 1
• Consider pregnancy in women of childbearing age 3, 4
• Screen for cannabis use - Cannabis Hyperemesis Syndrome should be suspected in heavy users, though treatment remains effective even with ongoing use 1

Stepwise Pharmacologic Algorithm

First-Line: Dopamine Receptor Antagonists

Initiate one of the following agents, titrated to maximum benefit and tolerance: 1, 2

• Metoclopramide 10 mg PO/IV three times daily (particularly effective for gastric stasis and can be increased to 20 mg per dose) 5, 1, 6
• Prochlorperazine 5-10 mg PO three to four times daily (usual adult dosing, not to exceed 40 mg daily in resistant cases) 5, 6
• Haloperidol 0.5-2 mg PO/IV every 4-6 hours (alternative dopamine antagonist with different receptor profile) 1, 2

These agents work centrally and peripherally to block dopamine receptors involved in the emetic pathway 5, 3.

Second-Line: Add 5-HT3 Antagonist

If symptoms persist after 4 weeks of dopamine antagonist therapy, add (do not replace) ondansetron 8 mg PO twice daily to target different receptor pathways for synergistic effect 1, 2, 7. The FDA-approved dosing for moderately emetogenic conditions is 8 mg administered initially, with a subsequent 8 mg dose 8 hours after the first dose, then 8 mg twice daily 7.

Critical monitoring: Watch for QTc prolongation when using ondansetron, especially in patients with electrolyte abnormalities (hypokalemia, hypomagnesemia), congestive heart failure, or those taking other QT-prolonging medications 1, 7.

Administration Strategy

• Schedule antiemetics around-the-clock rather than as-needed - prevention is far easier than treating established vomiting 2
• Use agents from different drug classes simultaneously rather than sequential monotherapy, as no single agent has proven superior for breakthrough symptoms 2
• Consider alternate routes (rectal suppositories, sublingual formulations) if oral route is not feasible due to active vomiting 2

Supportive Care Measures

• Ensure adequate fluid intake of at least 1.5 L/day 1
• Recommend small, frequent meals and avoidance of trigger foods 1, 3
• Correct electrolyte abnormalities, particularly hypokalemia and hypomagnesemia 1
• Consider thiamin supplementation to prevent Wernicke's encephalopathy in patients with persistent vomiting 1

Special Considerations for Specific Causes

If Gastroparesis or Gastritis is Suspected:

• Continue metoclopramide as it promotes gastric emptying 1
• Add proton pump inhibitor or H2 receptor antagonist 1

If Infectious Gastroenteritis:

• Ondansetron may facilitate oral rehydration but can increase stool volume/diarrhea 5, 1
• Prioritize fluid and electrolyte replacement over antiemetics 5

Critical Pitfalls to Avoid

• Never use antiemetics in suspected mechanical bowel obstruction 1, 2
• Monitor for extrapyramidal symptoms with dopamine antagonists, particularly in young males - treat with diphenhydramine 50 mg IV if they develop 1, 2
• Avoid repeated endoscopy or imaging unless new symptoms develop 1
• Do not delay treatment for extensive diagnostic workup in acute, mild cases without alarm symptoms 3, 8

When to Escalate Treatment

If symptoms remain refractory despite around-the-clock dopamine antagonist plus 5-HT3 antagonist:

• Add dexamethasone 10-20 mg IV in combination with ondansetron (this combination is superior to either agent alone) 1
• Consider continuous IV or subcutaneous infusions of antiemetics 2
• Trial dronabinol 2.5-7.5 mg PO every 4 hours as needed (FDA-approved cannabinoid for refractory nausea) 1
• Consider acupuncture (particularly electroacupuncture) when standard antiemetics fail 2