Prescription for acute onset vomiting
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Prescription for Acute Onset Vomiting
Initial Assessment
Before prescribing, identify the likely cause — this guides drug choice (Harrison's, p. 1218):
| Pattern | Likely Cause |
|---|---|
| Within 1 hr of eating | Gastroparesis, pyloric obstruction, rumination |
| Minutes after eating | Rumination syndrome |
| With diarrhea + fever | Acute gastroenteritis / infectious |
| With abdominal pain | Bowel obstruction, pancreatitis, cholecystitis |
| Hematemesis | Ulcer, Mallory-Weiss, malignancy |
| Drug/toxin history | Medication-induced |
Antiemetic Drug Choices
1. Ondansetron (5-HT₃ Antagonist) — First-line for most acute vomiting
- Adults: 4–8 mg PO/IV/IM every 8 hours PRN
- Children >4 yrs: 0.1–0.15 mg/kg PO (max 4 mg) — facilitates oral rehydration in gastroenteritis
- Route: Oral disintegrating tablet (ODT) useful when patient cannot swallow
- Guideline-supported for acute gastroenteritis in children >4 yrs (Infectious Diarrhea Guidelines, p. 9)
2. Metoclopramide (Dopamine Antagonist / Prokinetic)
- Dose: 10 mg PO/IV/IM every 6–8 hours
- Use: Especially useful when gastroparesis is suspected; also reduces nausea
- Caution: Extrapyramidal side effects (dystonia); avoid prolonged use
3. Domperidone (where available)
- Dose: 10 mg PO TDS, 15–30 min before meals
- Preferred prokinetic in some regions due to fewer CNS side effects than metoclopramide
4. Promethazine (Phenothiazine)
- Dose: 12.5–25 mg PO/IM every 4–6 hours
- Use: Motion sickness, vestibular causes, post-op nausea
- Caution: Sedation; contraindicated in children <2 years
5. Prochlorperazine
- Dose: 5–10 mg PO/IM TDS–QID (adult)
- Useful for severe nausea/vomiting when IV access is unavailable
6. Dexamethasone (adjunct)
- Dose: 4–8 mg IV (single dose)
- Useful in chemotherapy-induced or severe refractory vomiting
Fluid & Electrolyte Replacement (Essential)
Antiemetics are adjuncts, not substitutes for rehydration (Infectious Diarrhea Guidelines, p. 9):
- Mild–moderate dehydration: Oral rehydration solution (ORS) — sips every 5–10 min
- Severe dehydration / unable to tolerate oral: IV Normal Saline or Ringer's Lactate
- Monitor and replace potassium losses (vomiting depletes K⁺)
Special Situations
| Situation | Preferred Agent |
|---|---|
| Gastroenteritis (children >4 yrs) | Ondansetron ODT |
| Pregnancy (morning sickness) | Pyridoxine ± Doxylamine (first-line); Ondansetron (second-line) |
| Motion sickness / vestibular | Promethazine, Cinnarizine, Dimenhydrinate |
| Post-operative nausea | Ondansetron, Dexamethasone |
| Chemotherapy-induced | Ondansetron + Dexamethasone ± Aprepitant (NK1 antagonist) |
| Diabetic gastroparesis | Metoclopramide, Domperidone |
Red Flags — Refer / Investigate Further
- Signs of bowel obstruction (distension, obstipation)
- Hematemesis
- Severe abdominal rigidity
- Neurological symptoms (raised ICP, meningism)
- Severe dehydration / electrolyte imbalance
- No improvement after 24–48 hrs of treatment
Key principle: Treat the underlying cause alongside symptomatic antiemetic therapy. Antiemetics alone are insufficient if a surgical, metabolic, or serious infectious etiology is present.
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