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

First-Line Treatment for Nausea and Vomiting

Dopamine receptor antagonists (metoclopramide, prochlorperazine, or haloperidol) are the recommended first-line treatment for persistent nausea and vomiting, titrated to maximum benefit and tolerance. 1

Initial Assessment Before Treatment

Before initiating antiemetic therapy, identify and treat underlying reversible causes:

• Medication-induced causes: Review all current medications, particularly opioids, antibiotics, and chemotherapy agents 1, 2
• Gastritis or gastroesophageal reflux: Add proton pump inhibitors or H2 receptor antagonists if suspected 1, 2
• Severe constipation or fecal impaction: Rule out with abdominal examination and treat if present 1
• Metabolic abnormalities: Check for hypercalcemia, hypokalemia, hypochloremia, and metabolic alkalosis 1, 3
• Bowel obstruction: Never use antiemetics if mechanical bowel obstruction is suspected, as this can mask progressive ileus and gastric distension 1, 3

First-Line Pharmacologic Treatment Algorithm

Step 1: Dopamine Receptor Antagonists

Start with one of the following dopamine antagonists:

• Metoclopramide 10 mg PO/IV three times daily (particularly effective for gastric stasis and gastroparesis) 1, 3
• Prochlorperazine 10 mg PO/IV every 6-8 hours 1
• Haloperidol 0.5-2 mg PO/IV every 4-6 hours (alternative with different receptor profile) 1, 3

Critical monitoring: Watch for extrapyramidal side effects (akathisia, dystonia) with all dopamine antagonists, particularly in young males and within 48 hours of administration 3, 4. Treat extrapyramidal symptoms immediately with diphenhydramine 50 mg IV 3.

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

If vomiting continues after 4 weeks of dopamine antagonist therapy, add:

• Ondansetron 8 mg PO/IV 2-3 times daily (acts on different receptors, providing complementary coverage) 1, 3, 5
• Alternative: Granisetron 1 mg PO twice daily 2

Key principle: Add agents from different drug classes rather than replacing one antiemetic with another, as different neuroreceptors are involved in the emetic response 3. Ondansetron is particularly advantageous as it is not associated with sedation or akathisia 4.

Step 3: Additional Agents for Refractory Symptoms

If nausea and vomiting persist despite combination therapy, consider adding:

• Olanzapine 2.5-5 mg PO daily (especially effective for breakthrough vomiting in palliative care settings) 1, 2, 3
• Anticholinergic agents or antihistamines 1
• Cannabinoids (dronabinol 2.5-7.5 mg PO every 4 hours as needed for refractory cases) 1, 3
• Corticosteroids (dexamethasone 10-20 mg IV, particularly effective when combined with ondansetron) 1, 3

Special Considerations and Context-Specific Modifications

Anxiety-Related Nausea

• Add lorazepam 0.5-1 mg PO/IV every 4-6 hours 1, 2
• Caution: Avoid long-term benzodiazepine use due to dependence risk 1

Elderly Patients

• Reduce initial doses by 25-50% (e.g., lorazepam 0.25 mg, metoclopramide 5 mg) 2
• Elderly patients are especially sensitive to benzodiazepines and antipsychotics 2
• Monitor closely for extrapyramidal effects and cognitive impairment 2

Chemotherapy-Induced Nausea and Vomiting

• Follow specific NCCN antiemesis guidelines rather than general approaches 6, 1
• For breakthrough symptoms despite optimal prophylaxis, add olanzapine if not already receiving it 6

Cannabis Hyperemesis Syndrome

• Suspect in young adults with heavy cannabis use preceding symptom onset 3
• Do not stigmatize patients; offer abortive therapy even with ongoing use, as treatments can still be effective 3
• Definitive diagnosis requires 6 months of cannabis cessation 3

Administration Strategies

• Administer antiemetics on a scheduled basis rather than PRN, as prevention is far easier than treating established vomiting 3
• Consider alternative routes (IV, rectal suppositories, sublingual tablets) if oral route is not feasible due to ongoing vomiting 1, 3
• Ondansetron sublingual tablets may improve absorption in actively vomiting patients 1

Critical Pitfalls to Avoid

• Never use antiemetics in suspected mechanical bowel obstruction 1, 3
• Monitor QTc prolongation when using ondansetron, especially in combination with other QT-prolonging agents 3
• Avoid repeated endoscopy or imaging unless new symptoms develop 3
• Do not use sequential monotherapy; multiple concurrent agents from different classes are more effective for refractory cases 3
• Ensure adequate hydration and correct electrolyte abnormalities (particularly hypokalemia and hypomagnesemia) before and during treatment 1, 3

Supportive Care Measures

• Ensure adequate fluid intake of at least 1.5 L/day 3
• Small, frequent meals with dietary modifications 3
• Thiamin supplementation to prevent Wernicke's encephalopathy in patients with persistent vomiting 3