What is the recommended dose and administration protocol for thiamine (Vitamin B1) injections in a patient with suspected thiamine deficiency, possibly due to alcohol use disorder, gastrointestinal disorders, or malnutrition?

Thiamine (Vitamin B1) Injection Dosing

For suspected thiamine deficiency in the context of alcohol use disorder, malnutrition, or gastrointestinal disorders, administer 100-300 mg IV thiamine daily for 3-4 days, with higher doses of 500 mg IV three times daily (total 1,500 mg/day) reserved for established or suspected Wernicke's encephalopathy. 1

Critical Timing Consideration

• Thiamine must be administered BEFORE any glucose-containing IV fluids to prevent precipitating acute Wernicke's encephalopathy, as glucose metabolism requires thiamine as a cofactor and can rapidly deplete remaining stores 1, 2
• In emergency hypoglycemia, give thiamine concurrently with or immediately after glucose correction, but do not delay life-saving glucose 1

Dosing Algorithm by Clinical Scenario

Established or Suspected Wernicke's Encephalopathy

• 500 mg IV three times daily (total 1,500 mg/day) for at least 3-5 days 1, 3
• Classic triad: confusion, ataxia, ophthalmoplegia (though only 10-16% present with all three) 1
• Any encephalopathy of uncertain etiology in at-risk patients warrants this dose 1

High-Risk Patients Without Encephalopathy

• 100-300 mg IV daily for 3-4 days 1, 2
• High-risk includes: alcohol use disorder with malnutrition, prolonged vomiting, post-bariatric surgery, critical illness, unexplained lactic acidosis 1, 4
• 30-80% of alcohol-dependent individuals show thiamine deficiency 1

Refeeding Syndrome Prevention

• 300 mg IV BEFORE initiating nutrition therapy, then 200-300 mg IV daily for at least 3 more days 1
• Critical in malnourished patients about to receive nutrition support 1

Alcohol Withdrawal Management

• 100-300 mg IV daily if hospitalized or high-risk (malnourished, severe withdrawal) 1
• 100 mg oral daily for all patients undergoing alcohol withdrawal as routine care 1
• Continue for 2-3 months following resolution of withdrawal symptoms 1

Route Selection: IV vs. Oral

IV Route is Mandatory When:

• Active alcohol withdrawal or suspected acute deficiency 1
• Alcohol-related gastritis (poor absorption) 1
• Active vomiting or severe dysphagia 1
• Critical illness or hospitalized patients 1
• Any neurological symptoms in at-risk patients 1, 2
• Before administering IV dextrose to individuals with marginal thiamine status 2

Oral Route is Adequate When:

• Suspected chronic deficiency without acute disease 1
• Patient can reliably take oral medications 1
• Outpatient maintenance after IV loading 1

Transition to Oral Maintenance

• After completing 3-5 days of IV thiamine, transition to 50-100 mg oral daily for 2-3 months 1
• For patients who had Wernicke's encephalopathy, extend to 100-500 mg oral daily for 12-24 weeks 1
• Standard multivitamins (1-3 mg thiamine) are inadequate for deficiency treatment 1

Special Populations

Post-Bariatric Surgery

• 200-300 mg IV daily immediately for prolonged vomiting or poor intake 1
• Prophylactic 50 mg oral once or twice daily during first 3-4 months postoperatively 1

Chronic Diuretic Therapy

• 50 mg oral daily as prophylaxis to prevent deficiency 1
• 6% of ambulatory heart failure patients are thiamine deficient 1

Critical Illness/Sepsis

• 100-300 mg IV daily as >90% of critically ill patients are thiamine deficient or depleted 1, 4

Diagnostic Testing

• Do NOT wait for laboratory confirmation to treat - thiamine reserves deplete within 20 days and treatment is safe with no toxicity risk 1, 5
• If testing is performed, measure red blood cell (RBC) or whole blood thiamine diphosphate (ThDP) - NOT plasma thiamine 1
• Plasma thiamine is unreliable; only RBC/whole blood ThDP is valid 1

Safety Profile

• No established upper limit for toxicity - excess is excreted in urine 1, 2
• High IV doses rarely cause anaphylaxis 1
• Doses >400 mg may induce mild nausea, anorexia, or mild ataxia 1
• Treatment is safe, inexpensive, and potentially life-saving 5

Common Pitfalls to Avoid

• Giving glucose before thiamine - can precipitate irreversible Wernicke's encephalopathy 1, 2
• Underdosing - using only 10-100 mg in high-risk patients is inadequate 1
• Relying on standard multivitamins - contain only 1-3 mg, insufficient for treatment 1
• Stopping too early - tissue stores require months to replenish; 49% show incomplete recovery with inadequate treatment duration 1
• Using oral route in acute settings - absorption is impaired in alcohol use disorder, vomiting, or critical illness 1, 3

Evidence Quality Note

The guideline recommendations are consistent across multiple high-quality sources 1, 2, 3, though some evidence is based on clinical consensus rather than randomized trials due to the ethical impossibility of withholding treatment in suspected deficiency 1. The benefit-risk ratio is overwhelmingly favorable given thiamine's safety profile and the severity of untreated deficiency 1, 5.