What is the first line of treatment for a patient experiencing nausea and vomiting?

First-Line Treatment for Nausea and Vomiting

For patients experiencing nausea and vomiting, dopamine receptor antagonists (metoclopramide, prochlorperazine, or haloperidol) should be initiated as first-line therapy, titrated to maximum benefit and tolerance. 1

Initial Assessment Before Treatment

Before starting antiemetics, identify and address reversible causes:

• Rule out mechanical bowel obstruction through endoscopic or fluoroscopic evaluation—antiemetics are contraindicated in this setting as they can mask progressive ileus 2, 1
• Check for metabolic abnormalities: hypercalcemia, hypokalemia, hypochloremia, hypothyroidism, and Addison's disease 3
• Review all medications for potential adverse effects causing nausea 1
• Assess for gastroparesis or gastroesophageal reflux: if present, add proton pump inhibitors or H2 receptor antagonists 1
• Consider cannabis hyperemesis syndrome in younger patients with heavy cannabis use 3

Stepwise Treatment Algorithm

Step 1: First-Line Dopamine Receptor Antagonists

Start with one of the following 1:

• Metoclopramide 10 mg orally three times daily before meals (particularly effective for gastroparesis) 1, 3
• Prochlorperazine 10 mg orally or IV every 6-8 hours 1
• Haloperidol 1 mg orally or IV every 4 hours as needed 3

Critical pitfall: Monitor for extrapyramidal side effects (akathisia, dystonia), especially in young males—treat with diphenhydramine 50 mg IV if they develop 3, 4

Step 2: Add 5-HT3 Receptor Antagonist if Symptoms Persist

If vomiting continues after 4 weeks of dopamine antagonist therapy 3:

• Add ondansetron 8 mg orally 2-3 times daily or 8-16 mg IV 1, 3, 5
• Ondansetron is FDA-approved for chemotherapy-induced, radiation-induced, and postoperative nausea/vomiting 5
• Use sublingual formulation if oral route is compromised by active vomiting 1
• Monitor QTc interval when combining with other QT-prolonging agents 3

Key principle: Add agents from different drug classes rather than replacing one antiemetic with another, as different neuroreceptors mediate the emetic response 1, 3

Step 3: Additional Agents for Refractory Symptoms

If nausea persists despite combination therapy, add one or more of the following 1:

• Olanzapine (superior efficacy for breakthrough vomiting in some studies) 1, 3
• Dexamethasone 10-20 mg IV (synergistic with ondansetron, category 1 evidence) 3
• Anticholinergic agents or antihistamines (promethazine, diphenhydramine) 1
• Cannabinoids (dronabinol 2.5-7.5 mg orally every 4 hours) 1, 3
• Benzodiazepines (lorazepam) for anxiety-related nausea 1

Step 4: Route of Administration Considerations

• Administer antiemetics on a scheduled basis rather than as-needed—prevention is more effective than treating established vomiting 3
• Use alternative routes when oral intake is not feasible: IV, rectal suppositories, or sublingual formulations 1, 3
• Consider continuous IV or subcutaneous infusion for severe refractory cases 1

Supportive Care Measures

• Ensure adequate hydration: at least 1.5 L/day fluid intake 3
• Correct electrolyte abnormalities: particularly hypokalemia, hypomagnesemia, and hypochloremia from prolonged vomiting 3
• Provide thiamin supplementation to prevent Wernicke's encephalopathy in persistent vomiting 3
• Recommend dietary modifications: small, frequent meals and avoidance of trigger foods 3

Context-Specific Considerations

Chemotherapy-Induced Nausea and Vomiting

Follow specific antiemesis guidelines rather than general approaches—typically requires NK1 receptor antagonist, 5-HT3 antagonist, and dexamethasone combination 2

Radiation-Induced Nausea and Vomiting

For high-emetic-risk radiation: 5-HT3 antagonist plus dexamethasone before each fraction 2

Postoperative Nausea and Vomiting

Ondansetron 16 mg administered 1 hour before induction of anesthesia 5

Common Pitfalls to Avoid

• Never use antiemetics in suspected mechanical bowel obstruction without first ruling it out 1
• Avoid droperidol except for refractory cases due to FDA black box warning for QT prolongation 4
• Do not use promethazine IV without caution due to risk of vascular damage 4
• Monitor for tardive dyskinesia with long-term metoclopramide use (FDA black box warning) 1
• Avoid repeated endoscopy or imaging unless new symptoms develop 3