What is the initial treatment approach for vomiting in a healthy adult?

Initial Treatment of Vomiting in Healthy Adults

For acute vomiting in healthy adults, ondansetron (5-HT3 antagonist) is the preferred first-line antiemetic, with fluid and electrolyte replacement initiated concurrently as the cornerstone of management. 1, 2

Immediate Management Priorities

Fluid Resuscitation

• Fluid and electrolyte replacement takes priority over antiemetic therapy alone and should be initiated before or concurrent with antiemetic administration 1
• For patients who can tolerate oral intake: Use oral rehydration with small, frequent sips of electrolyte-rich fluids (sports drinks) 2
• For moderate-severe dehydration or inability to tolerate oral intake: Initiate IV fluid therapy with normal saline or lactated Ringer's solution, starting with a 500-1000 mL bolus followed by maintenance rate 2
• Continue oral rehydration even with ongoing emesis, as most fluid is retained 1

First-Line Antiemetic Therapy

• Ondansetron is the preferred initial agent due to superior efficacy and safety profile with no sedation or extrapyramidal side effects 1, 2, 3
• Dosing: 8 mg administered orally, with sublingual formulation potentially improving absorption in actively vomiting patients 2, 4
• Available formulations include oral, sublingual, and IV, providing flexibility based on patient tolerance 1

Alternative Antiemetic Options

Second-Line Agents (if ondansetron fails or is contraindicated)

• Promethazine 12.5-25 mg IV/IM/rectal: More sedating than other agents; suitable when sedation is desirable but avoid during oral rehydration as sedation interferes with fluid intake 2, 3
• Prochlorperazine 10 mg IV/IM or 25 mg rectal suppository: Effective but monitor for akathisia that can develop any time over 48 hours post-administration 2, 3
• Metoclopramide 10 mg IV/IM: Monitor for akathisia; decreasing infusion rate reduces incidence of this adverse effect, treatable with IV diphenhydramine 2, 3

Refractory Vomiting

• For refractory cases, consider combination therapy with a benzodiazepine (lorazepam 0.5-1 mg IV or alprazolam 0.25-0.5 mg sublingual) plus haloperidol 0.5-2 mg IV, with monitoring for QT prolongation 2

Critical Safety Considerations

Ondansetron Precautions

• Avoid in patients with congenital long QT syndrome 4
• ECG monitoring recommended in patients with electrolyte abnormalities (hypokalemia, hypomagnesemia), congestive heart failure, bradyarrhythmias, or those taking QT-prolonging medications 4
• Contraindicated with concomitant apomorphine due to risk of profound hypotension and loss of consciousness 4
• Monitor for hypersensitivity reactions including anaphylaxis and bronchospasm; discontinue if these occur 4

Medications to Avoid

• Do not use antimotility agents (loperamide) in patients with fever, bloody diarrhea, or risk of toxic megacolon 1

Common Pitfalls

• Failing to prioritize fluid resuscitation: Antiemetics alone are insufficient; dehydration correction is essential 1
• Premature discontinuation of oral fluids: Most oral fluid is retained even with ongoing vomiting 1
• Not monitoring for delayed akathisia: With prochlorperazine and metoclopramide, akathisia can develop up to 48 hours after administration 3
• Overlooking QT prolongation risk: Multiple antiemetics (ondansetron, haloperidol) can prolong QT interval, requiring ECG monitoring in at-risk patients 2, 4