Can an otherwise healthy adult patient who started Lexapro (escitalopram) 10 mg today and now has three days of nausea, vomiting, dry retching, diarrhea and intermittent hot‑cold sensations, without fever, allergies, QT‑prolongation risk or pregnancy, be safely prescribed ondansetron and receive a medical certificate?

Can This Patient Receive Ondansetron?

Yes, this patient can safely receive ondansetron for acute gastroenteritis with nausea and vomiting, as she has no contraindications (no cardiac conduction abnormalities, QT prolongation, pregnancy, or drug allergies), and ondansetron is recommended as first-line therapy for facilitating oral rehydration in adults with acute gastroenteritis. 1, 2, 3

Clinical Assessment

This patient presents with:

• Three days of nausea, vomiting, dry retching, and diarrhea consistent with acute viral gastroenteritis 2
• New onset of Lexapro (escitalopram) 10 mg this morning, which likely exacerbated pre-existing gastroenteritis symptoms rather than causing them 4
• No fever, no bloody diarrhea, no signs of severe dehydration 2
• No cardiac history, no QT-prolonging medications (Lexapro does not significantly prolong QT), and no allergies 4, 5

Ondansetron Dosing Regimen

For acute gastroenteritis in adults, prescribe ondansetron 8 mg orally every 8 hours as needed for ongoing nausea and vomiting. 2

• Start with 8 mg orally immediately, then repeat every 8 hours as needed 2
• Maximum daily dose should not exceed 24 mg per day 1
• If nausea persists despite as-needed dosing, switch to scheduled administration (8 mg every 8 hours) for 24-48 hours to maintain steady therapeutic levels 1, 2

Safety Considerations

Ondansetron is the safest first-line antiemetic for this patient because it lacks sedation, does not cause akathisia (unlike metoclopramide or prochlorperazine), and has no interaction with escitalopram. 3

However, be aware of these precautions:

• QT prolongation risk: While ondansetron can prolong the QT interval, this is primarily a concern at the 32 mg IV dose used in chemotherapy, not at the 8 mg oral doses used for gastroenteritis 5
• Baseline ECG is not required for this healthy young patient at standard oral doses 1
• Ondansetron may cause constipation, which could be problematic if the diarrhea resolves 1
• Rare hypersensitivity reactions have been reported, though uncommon 6

Adjunctive Management

In addition to ondansetron, this patient requires:

• Oral rehydration solution (ORS): Administer small, frequent volumes (5-10 mL every 1-2 minutes) to prevent triggering more vomiting 2, 7
• Resume normal diet: Continue eating age-appropriate foods immediately; do not fast 7
• Avoid caffeine: Coffee, tea, and caffeinated sodas worsen diarrhea through stimulation of intestinal motility 7
• Avoid high-sugar beverages: Sports drinks and fruit juices can exacerbate osmotic diarrhea 7

Lexapro Management

Advise the patient to reduce Lexapro to 5 mg daily for 1-2 weeks, then increase to 10 mg as tolerated, since nausea is a common early side effect that typically resolves within 1-2 weeks. 1

• The current nausea is likely multifactorial: primarily gastroenteritis with Lexapro contributing 4
• Nausea from SSRIs typically improves with continued use or dose reduction 4

If Ondansetron Fails

If nausea persists despite ondansetron, add (do not replace) a dopamine antagonist with a different mechanism of action: 1

• Metoclopramide 10 mg orally every 6 hours (highest evidence for efficacy; also provides prokinetic benefit) 1
• Prochlorperazine 10 mg orally every 6 hours (alternative if metoclopramide causes akathisia) 1
• Monitor for akathisia within the first 48 hours; treat with diphenhydramine 50 mg if it occurs 1, 3

Consider adding dexamethasone 4-8 mg orally once daily if nausea remains refractory after 24-48 hours of combination therapy. 1

Red Flags Requiring Reassessment

Instruct the patient to return immediately if she develops: 2, 7

• Bloody diarrhea (suggests bacterial infection requiring stool culture) 2, 7
• Signs of severe dehydration (altered mental status, prolonged skin tenting, decreased urine output) 7
• High fever >38.5°C with systemic toxicity 7
• Severe abdominal pain disproportionate to examination 7
• Inability to tolerate any oral fluids despite ondansetron 7

Medical Certificate

Provide a medical certificate for 2-3 days off work, as acute gastroenteritis typically resolves within 3-5 days with appropriate supportive care. 7

Common Pitfalls to Avoid

• Do not use metoclopramide as first-line therapy: It has fair evidence of being ineffective in gastroenteritis and causes more side effects than ondansetron 7, 3
• Do not use loperamide: Antimotility agents are not recommended in acute gastroenteritis and do not reduce symptom duration 7
• Do not delay rehydration: Start ORS immediately; ondansetron facilitates oral rehydration but does not replace it 2, 7
• Do not use IV ondansetron: Oral administration is equally effective and avoids the higher QT prolongation risk associated with IV dosing 5