Thiamine Dosing in Hyperemesis Gravidarum
For hyperemesis gravidarum with prolonged vomiting, administer thiamine 300 mg daily orally along with two vitamin B compound strong tablets three times daily; if vomiting persists or the patient cannot tolerate oral intake, switch immediately to intravenous thiamine 200-300 mg daily. 1
Risk Assessment and Prevention Strategy
Pregnancy itself increases thiamine requirements, and hyperemesis gravidarum rapidly depletes thiamine stores within 7-8 weeks of persistent vomiting 1, 2. Thiamine reserves can be completely exhausted after only 20 days of inadequate oral intake 1, making early supplementation critical to prevent Wernicke's encephalopathy, which carries a 5% maternal mortality risk and 65% risk of permanent cognitive impairment 2.
High-Risk Indicators Requiring Immediate IV Thiamine:
- Weight loss ≥12 kg or ≥5% of pre-pregnancy body weight 2, 3
- Vomiting duration >7 weeks 2
- Any neurological symptoms (visual changes, nystagmus, ataxia, confusion, altered mental status) 2, 4
- Ketonuria with dehydration 3, 4
- Patients receiving IV glucose or parenteral nutrition (glucose administration without thiamine can precipitate acute Wernicke's encephalopathy) 2, 5
Treatment Algorithm by Clinical Severity
Mild to Moderate Hyperemesis (Outpatient Management)
- Thiamine 300 mg orally daily 1
- Plus vitamin B compound strong: 2 tablets three times daily 1
- Continue until vomiting resolves and oral intake is adequate 1
Severe Hyperemesis or Inability to Tolerate Oral Intake
- Thiamine 200-300 mg IV daily for at least 3-5 days 1
- Switch to oral maintenance (50-100 mg daily) once vomiting controlled 1
Suspected or Confirmed Wernicke's Encephalopathy
- Thiamine 500 mg IV three times daily (1,500 mg total daily dose) 1, 4
- Continue high-dose IV therapy until complete neurological recovery 4
- Critical: Administer thiamine BEFORE any IV glucose to prevent acute deterioration 2
- Taper to oral thiamine and continue throughout pregnancy 4
Patients on Total Parenteral Nutrition
- Minimum 2.5 mg/day thiamine in PN formulation 1
- However, for hyperemesis gravidarum specifically, provide 200-300 mg daily given the increased metabolic demands and depletion risk 1
- Verify thiamine is included in PN formulation, as iatrogenic Wernicke's encephalopathy from thiamine-deficient PN has been reported 5, 6
Monitoring Requirements
Check thiamine status (RBC or whole blood thiamine diphosphate) every trimester in all hyperemesis gravidarum patients 1, particularly those with:
- Persistent vomiting beyond first trimester 2
- Inadequate weight gain or continued weight loss 1
- Any visual or neurological complaints 4
Critical Clinical Pitfalls to Avoid
Never administer IV dextrose before thiamine replacement in at-risk patients—this can precipitate acute Wernicke's encephalopathy with potentially irreversible consequences 2. The systematic review found that 14% of Wernicke's cases were directly exacerbated by glucose administration without thiamine 2.
Do not rely on the classic triad (ophthalmoplegia, ataxia, altered mental status) for diagnosis—only a minority of patients present with all three features 2, 4. Prodromal symptoms include persistent vomiting (100%), diplopia (37%), and blurred vision (27%) 2.
Subtherapeutic dosing is common and dangerous—64% of reported cases received inadequate thiamine doses, contributing to poor outcomes 2. When in doubt, higher doses are safe (no established upper limit, with only rare anaphylaxis at very high IV doses) 1.
Route Selection
Use IV or IM route for any acute presentation with severe vomiting, as oral absorption is unreliable in hyperemesis gravidarum 1. The ESPEN guidelines specifically state that "in case of acute disease, the suspicion of inadequate intake, even short term, should prompt the use of the IV route" 1.
Oral supplementation is adequate only for mild cases with controlled symptoms and reliable oral intake 1.