Thiamine Loading Protocol
For acute thiamine deficiency or high-risk situations, administer 100-300 mg IV daily for 3-4 days, escalating to 500 mg IV three times daily (1,500 mg/day total) if Wernicke encephalopathy is suspected or confirmed. 1, 2
Clinical Situation-Based Dosing Algorithm
Emergency/High-Risk Situations (IV Route Mandatory)
Established or Suspected Wernicke Encephalopathy:
- 500 mg IV three times daily for 3-5 days, then transition to oral 250-300 mg daily 1, 2, 3
- This includes encephalopathy of uncertain etiology where thiamine deficiency cannot be excluded 1
Critical Illness/ICU Admission:
- 100-300 mg IV daily from admission for 3-4 days without hesitation 1, 2
- Do not wait for laboratory confirmation—thiamine reserves deplete within 20 days of inadequate intake 2
Refeeding Syndrome:
- 300 mg IV as a single dose before initiating nutrition therapy, followed by 200-300 mg IV daily for at least 3 additional days 1, 2
- Critical to prevent Wernicke encephalopathy when restarting nutrition after prolonged fasting 2
Alcohol Use Disorder with High-Risk Features:
- High-risk features include malnutrition, severe withdrawal, vomiting, or any neurological signs 2, 4
- Administer 100-300 mg IV daily; escalate to 500 mg IV three times daily if Wernicke signs emerge 2, 4
- Continue for 2-3 months after withdrawal symptom resolution 2, 4
Moderate-Risk Situations
Hospitalized Patients with Suspected Reduced Intake:
- 100-300 mg daily, either oral or IV route depending on absorption capacity 1, 2
- Use IV route if alcohol-related gastritis, active vomiting, or acute illness present 1, 2
Chronic Diuretic Therapy:
- 50 mg oral daily as prophylaxis 1
Continuous Renal Replacement Therapy:
- 100 mg IV daily due to dialytic losses 1
Mild Deficiency (Outpatient)
Low Dietary Intake Without Acute Symptoms:
- 10 mg oral daily for one week, then 3-5 mg oral daily for at least 6 weeks 1, 2
- Maintenance dose after proven deficiency: 50-100 mg oral daily 1, 2
Critical Timing Considerations
Always administer thiamine BEFORE glucose-containing IV fluids to avoid precipitating acute Wernicke encephalopathy, as thiamine is essential for glucose metabolism 2, 3. In life-threatening hypoglycemia, give thiamine concurrently with or immediately after glucose correction 2.
For patients requiring parenteral nutrition after prolonged fasting, give thiamine as the first dose before commencing PN 2.
Route Selection Framework
Use IV route when:
- Acute disease or suspected acute deficiency present 1
- Alcohol-related gastritis (poor oral absorption) 1, 2
- Active vomiting or inability to take oral medications 2
- Any suspicion of Wernicke encephalopathy 1, 2
- Post-bariatric surgery with prolonged vomiting 2
Oral route adequate when:
- Chronic deficiency without acute disease 1
- Mild withdrawal in alcohol use disorder without complications 4
- Maintenance therapy after IV loading 1, 2
Common Pitfalls to Avoid
Do not use low doses (e.g., 100 mg once daily) for suspected Wernicke encephalopathy—this is grossly inadequate for acute neurological presentations requiring 500 mg three times daily 1, 2, 5.
Do not delay treatment waiting for laboratory confirmation—clinical suspicion alone warrants immediate treatment given the favorable benefit-risk ratio 2, 6. If laboratory confirmation needed, measure RBC or whole blood thiamine diphosphate (ThDP), not plasma thiamine 1, 5.
Do not administer glucose before thiamine in at-risk patients, as this can precipitate acute deficiency 2, 3.
Safety Profile
Thiamine has no established upper limit for toxicity, with excess excreted in urine 1, 2. High IV doses rarely cause anaphylaxis (no cases observed in a study of 463 doses of 500 mg IV push) 7. Doses exceeding 400 mg may induce mild nausea, anorexia, and mild ataxia 1, 2. Injection site reactions occur in less than 1% of administrations and are typically low-grade 7.
Duration of Treatment
- Acute loading: 3-5 days IV, then transition to oral maintenance 1, 2, 8
- Mild deficiency: Minimum 6 weeks oral therapy 1, 2
- Alcohol use disorder: 2-3 months following resolution of withdrawal symptoms 2, 4
- Post-bariatric surgery prophylaxis: First 3-4 months postoperatively 2
Special Populations
Post-Bariatric Surgery:
- Standard multivitamins insufficient; add thiamine 50 mg once or twice daily from B-complex supplement 2
- With prolonged vomiting or poor intake: 200-300 mg IV daily immediately 2
Parenteral Nutrition: