What is the initial management for an adult presenting with vomiting?

Initial Management of Vomiting in Adults

Begin with immediate fluid and electrolyte replacement as the cornerstone of management, taking priority over antiemetic therapy, and initiate ondansetron as the preferred first-line antiemetic agent. 1

Immediate Priorities

Fluid Resuscitation

• Fluid resuscitation must 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 2
• Administer a 500-1000 mL bolus followed by maintenance rate 2
• Add dextrose to IV fluids if prolonged fasting or concern for hypoglycemia exists 2

Laboratory Assessment

• Obtain complete blood count, serum electrolytes, glucose, liver function tests, lipase, and urinalysis to exclude metabolic causes and assess dehydration 3
• Monitor specifically for hypokalemia, hypochloremia, and metabolic alkalosis, which commonly result from prolonged vomiting 3
• Consider testing for hypercalcemia, hypothyroidism, and Addison's disease if clinically indicated 3
• Obtain urine drug screen to assess for cannabis use, particularly in younger adults 3

First-Line Antiemetic Therapy

Ondansetron (5-HT3 Antagonist)

• Ondansetron is the preferred initial agent for acute vomiting due to superior efficacy and safety profile 1, 2
• Use sublingual tablet formulation to potentially improve absorption in actively vomiting patients 2
• Ondansetron has no sedation or extrapyramidal side effects 1
• Available in oral, sublingual, and IV formulations for flexibility 1
• Monitor for QTc prolongation, especially when combined with other QT-prolonging agents 3, 2

Second-Line and Adjunctive Agents

If Ondansetron Fails or Is Contraindicated

• Promethazine 12.5-25 mg IV/IM/rectal 2
• Prochlorperazine 10 mg IV/IM or 25 mg rectal suppository 2
• Metoclopramide 10 mg IV/IM 2

For Refractory Vomiting

• Consider combination therapy with benzodiazepine (lorazepam 0.5-1 mg IV or alprazolam 0.25-0.5 mg sublingual) plus haloperidol 0.5-2 mg IV 2
• Monitor for QT prolongation with combination therapy 2

Stepwise Pharmacologic Approach for Persistent Symptoms

• Initiate dopamine receptor antagonists (metoclopramide, prochlorperazine, or haloperidol) titrated to maximum benefit and tolerance 3
• If symptoms persist after 4 weeks, add 5-HT3 antagonist such as ondansetron 3
• Monitor for extrapyramidal symptoms with dopamine antagonists, particularly in young males 3

Special Clinical Scenarios

Cyclic Vomiting Syndrome (CVS)

If stereotypical episodes of acute-onset vomiting lasting <7 days with episode-free intervals are present 4:

• Use standard abortive regimen: sumatriptan (nasal spray or subcutaneous) + ondansetron + benzodiazepine 1, 2
• Provide IV dextrose-containing fluids 1, 2
• Administer IV ketorolac as first-line non-narcotic analgesic 1
• Consider sedation with promethazine or lorazepam 2
• Place patient in quiet, dark environment to optimize response 2
• Obtain cannabis use history, as Cannabis Hyperemesis Syndrome should be suspected if heavy use preceded symptom onset 3

Gastroparesis or Gastritis Suspected

• Continue metoclopramide as it promotes gastric emptying 3
• Add proton pump inhibitor or H2 receptor antagonist 3

Critical Pitfalls to Avoid

• Never use antiemetics in suspected mechanical bowel obstruction, as this can mask progressive ileus and gastric distension 3
• Avoid antimotility agents (loperamide) in patients with fever, bloody diarrhea, or risk of toxic megacolon 1
• Do not avoid treatment in patients with ongoing cannabis use—abortive and prophylactic therapy can still be effective 3
• Avoid repeated endoscopy or imaging unless new symptoms develop 3
• Do not give prophylactic antiemetics in radiation exposure cases, as vomiting onset helps determine radiation dose 2

Supportive Care Measures

• Ensure adequate fluid intake of at least 1.5 L/day 3
• Recommend small, frequent meals 3
• Provide thiamin supplementation to prevent Wernicke's encephalopathy in patients with persistent vomiting 3
• Continue oral rehydration even with ongoing emesis, as most fluid is retained 1

When to Obtain Imaging

• Perform one-time esophagogastroduodenoscopy (EGD) or upper GI imaging to exclude obstructive lesions 3
• Avoid repeated endoscopy or imaging studies 3