What is the best course of treatment for a patient experiencing prolonged vomiting lasting 8 hours?

Management of Prolonged Vomiting Lasting 8 Hours

For a patient experiencing vomiting lasting 8 hours, initiate ondansetron 8 mg orally or sublingually immediately, ensure adequate hydration with oral rehydration solution or IV fluids if oral intake is not tolerated, and administer antiemetics on a scheduled basis rather than as-needed to prevent ongoing symptoms. 1, 2

Immediate Assessment and Stabilization

Hydration Status and Electrolyte Management

• Check for dehydration immediately by assessing vital signs, mucous membranes, skin turgor, and urine output 1
• Obtain serum electrolytes, glucose, and renal function tests to identify hypokalemia, hypochloremia, and metabolic alkalosis that commonly occur with prolonged vomiting 1
• Correct electrolyte abnormalities, particularly hypokalemia and hypomagnesemia, as these worsen nausea and can prolong QT interval when combined with ondansetron 1, 2

Rule Out Life-Threatening Causes

• Assess for bilious vomiting, abdominal distension, or absent bowel sounds that suggest bowel obstruction requiring immediate surgical consultation 1, 3
• Check for signs of increased intracranial pressure (headache, altered mental status, focal neurologic deficits) 4
• Consider metabolic causes including hypercalcemia, hypothyroidism, and Addison's disease if clinically indicated 1

First-Line Pharmacologic Management

Ondansetron as Primary Agent

• Administer ondansetron 8 mg orally or sublingually every 8 hours as the first-line antiemetic 1, 2
• Use sublingual formulation if oral route is compromised by ongoing vomiting 3
• The FDA-approved dosing for prevention of nausea and vomiting is 8 mg with subsequent doses every 8 hours 2

Critical Monitoring with Ondansetron

• Monitor for QT prolongation, especially in patients with electrolyte abnormalities (hypokalemia, hypomagnesemia), congestive heart failure, or those taking other QT-prolonging medications 1, 2
• Avoid ondansetron in patients with congenital long QT syndrome 2
• ECG monitoring is recommended in high-risk patients 2

Scheduled Dosing Strategy

Around-the-Clock Administration

• Administer antiemetics on a scheduled basis rather than PRN, as prevention of vomiting is far easier than treating established symptoms 5, 1
• Continue scheduled dosing for 1-2 days even after vomiting resolves to prevent recurrence 5, 2

Rehydration Protocol

Oral Rehydration Approach

• If patient can tolerate oral intake, provide oral rehydration solution in small, frequent amounts (1-3 ounces every 10-15 minutes) 6, 7
• Most fluid given orally is retained even if some vomiting occurs 8
• Wait 10 minutes after vomiting episode, then resume oral fluids more slowly 8

Intravenous Rehydration

• If oral intake is not tolerated after ondansetron administration, initiate IV isotonic crystalloid 20-30 mL/kg over 1-2 hours 6
• Reassess ability to tolerate oral fluids after IV rehydration 6
• Patients with serum bicarbonate ≤13 mEq/L are more likely to require continued IV therapy and hospitalization 6

Second-Line Therapy for Refractory Symptoms

Adding Dopamine Antagonists

• If vomiting persists after 4 hours of ondansetron therapy, add metoclopramide 10 mg IV/PO every 6 hours 1
• Metoclopramide is particularly effective for gastric stasis and promotes gastric emptying 1, 3
• Alternative dopamine antagonist: prochlorperazine 10 mg IV/PO every 6 hours 1

Combination Therapy

• Use agents from different drug classes simultaneously rather than sequential monotherapy, as no single agent has proven superior for breakthrough emesis 5, 1
• Consider adding dexamethasone 10-20 mg IV to ondansetron, as this combination is superior to either agent alone 1

Alternative Routes of Administration

When Oral Route Fails

• Use rectal suppositories (promethazine 25 mg or prochlorperazine 25 mg) if oral and IV routes are not feasible 3
• Consider sublingual ondansetron tablets for better absorption than standard tablets 3

Supportive Care Measures

Dietary Modifications

• Ensure adequate fluid intake of at least 1.5 L/day once vomiting is controlled 1
• Provide small, frequent meals rather than large meals 1, 3
• Recommend bland diet (bananas, rice, applesauce, toast) 5

Thiamin Supplementation

• Administer thiamin supplementation to prevent Wernicke's encephalopathy in patients with persistent vomiting 1, 3

Critical Pitfalls to Avoid

Contraindications and Warnings

• Never use antiemetics in suspected mechanical bowel obstruction, as this masks progressive ileus and worsens gastric distension 1, 3
• Do not use prokinetic agents (metoclopramide) if bowel obstruction is suspected 3
• Monitor for extrapyramidal symptoms (dystonia, akathisia) with dopamine antagonists, particularly in young males 1, 3
• Treat extrapyramidal symptoms immediately with diphenhydramine 50 mg IV if they develop 1

Avoid Repeated Testing

• Do not perform repeated endoscopy or imaging unless new symptoms develop 1
• One-time upper GI imaging or EGD is sufficient to exclude obstructive lesions 1

When to Escalate Care

Indications for Hospitalization

• Inability to tolerate oral fluids after IV rehydration and ondansetron administration 6
• Serum bicarbonate ≤13 mEq/L suggests more severe dehydration requiring prolonged IV therapy 6
• Bilious vomiting or signs of bowel obstruction 1, 3
• Altered mental status or signs of increased intracranial pressure 4
• Severe electrolyte abnormalities that cannot be corrected in outpatient setting 1