What medications are recommended for treating vomiting in adults and children over 4 years old, considering potential gastrointestinal disorders or risk of dehydration?

Medications for Vomiting

For adults and children over 4 years with vomiting, ondansetron is the first-line antiemetic medication, given at 0.15 mg/kg (maximum 16 mg/dose) intravenously or intramuscularly, or as an oral dissolving tablet. 1, 2, 3

Primary Treatment Approach

Oral rehydration must be initiated first before considering antiemetic medication, as small-volume oral rehydration solution (ORS) administration (5-10 mL every 1-2 minutes) successfully rehydrates over 90% of patients without any antiemetic medication. 2

Ondansetron: First-Line Antiemetic

Indications and Efficacy

• Ondansetron is recommended to facilitate oral rehydration in children >4 years of age and adolescents with acute gastroenteritis associated with vomiting when vomiting is significant enough to prevent adequate oral intake. 1, 3
• The Infectious Diseases Society of America recommends ondansetron may be given to adults after adequate hydration is achieved. 2
• Ondansetron reduces immediate need for hospitalization or intravenous rehydration, though it may increase stool volume as a side effect. 1
• In emergency department settings, ondansetron is as effective as promethazine and is not associated with sedation or akathisia, making it suitable as a first-line agent for most patient populations. 4

Dosing and Administration

• Weight-based dosing: 0.15 mg/kg per dose (maximum 16 mg per dose) for intramuscular or intravenous routes. 3
• Oral dissolving tablet (ODT) formulation is available and shows mean decrease in nausea score of 3.3 on a 10-point scale, though IV administration is more effective (mean decrease 4.4). 5
• Ondansetron is FDA-approved for pediatric patients 4 years and older for prevention of chemotherapy-induced nausea and vomiting. 6

Critical Safety Considerations

• Screen for cardiac history before administration, including congenital heart disease or arrhythmias, as ondansetron can prolong the QT interval. 2, 3, 6
• Special caution is warranted in children with underlying heart disease due to potential QT prolongation. 2, 3
• Avoid ondansetron in patients with bloody diarrhea, fever suggesting inflammatory/bacterial diarrhea, or suspected bacterial gastroenteritis. 2
• Ondansetron should only be used in children ≥6 months of age for acute gastroenteritis management. 3
• In severe hepatic impairment (Child-Pugh score ≥10), do not exceed a total daily dose of 8 mg. 6

Alternative Antiemetic Options

For Adults Only

• Promethazine 25 mg orally or rectally may be used when sedation is desirable, but it is more sedating than other agents and has potential for vascular damage with IV administration. 7, 4
• Metoclopramide 20 mg IV is an option, but patients must be monitored for akathisia that can develop at any time over 48 hours post-administration. 4, 8
• Prochlorperazine is another alternative, but similarly requires monitoring for dystonic reactions and akathisia. 1
• Droperidol was commonly used in the past and is more effective than prochlorperazine or metoclopramide, but due to FDA black box warning regarding QT prolongation, its use is limited to refractory cases. 4

Chemotherapy-Induced Vomiting (Specialized Context)

• For high-emetic-risk chemotherapy, a four-drug combination of NK₁ receptor antagonist (aprepitant), 5-HT₃ receptor antagonist, dexamethasone, and olanzapine is recommended. 1
• For moderate-emetic-risk chemotherapy with carboplatin (AUC ≥4 mg/mL per minute), a three-drug combination of NK₁ receptor antagonist, 5-HT₃ receptor antagonist, and dexamethasone is recommended. 1

Medications NOT Recommended

• Antimotility agents (loperamide) should never be given to children under 18 years with acute diarrhea, as deaths have been reported in 0.54% of children given loperamide, all occurring in children <3 years old. 1, 9
• Loperamide should be avoided in suspected or proven cases where toxic megacolon may result, including inflammatory diarrhea or diarrhea with fever. 1
• Metoclopramide is explicitly not recommended for gastroenteritis (Grade D recommendation: fair evidence that it is ineffective or harms outweigh benefits), as it is a prokinetic agent that increases gastrointestinal motility, which is counterproductive in acute diarrheal illness. 9
• Adsorbents, antisecretory drugs, and toxin binders should be avoided as they do not demonstrate effectiveness in reducing diarrhea volume or duration. 2, 9

Common Pitfalls to Avoid

• Do not use antiemetics as a substitute for appropriate fluid and electrolyte therapy, which remains the mainstay of treatment. 3
• Do not give ondansetron to children under 4 years of age for acute gastroenteritis, as a recommendation cannot be made for routine use in this age group. 1
• Do not use promethazine in children under 2 years of age, as it is contraindicated. 7
• Antiemetics should not be used in vomiting of unknown etiology in children and adolescents until appropriate evaluation is completed. 7
• Do not delay rehydration therapy while awaiting antiemetic medication, as oral rehydration should be initiated promptly with small-volume, frequent administration. 2, 9