What are the recommended thiamine (vitamin B1) dosing regimens for patients with suspected or confirmed deficiency, including acute Wernicke’s encephalopathy, chronic alcohol use, malnutrition, bariatric surgery, prolonged parenteral nutrition, and prophylaxis?

Thiamine Dosing Recommendations

For suspected or confirmed thiamine deficiency, administer 500 mg IV three times daily (1,500 mg/day total) for established Wernicke's encephalopathy, 100-300 mg IV daily for high-risk patients with malnutrition or alcohol use disorder, and always give thiamine before any glucose-containing fluids to prevent precipitating acute encephalopathy. 1

Acute Wernicke's Encephalopathy

Administer 500 mg IV thiamine three times daily for at least 3-5 days for any patient with established or suspected Wernicke's encephalopathy (confusion, ataxia, ophthalmoplegia). 1 This aggressive dosing is necessary because lower doses are inadequate for patients with severe neurological involvement. 1

• After the initial 3-5 day IV course, transition to oral thiamine 100-500 mg daily for 12-24 weeks to complete treatment and allow tissue stores to fully replenish. 1
• Approximately 49% of patients show incomplete recovery and 19% have permanent cognitive impairment even with treatment, so early aggressive therapy is critical. 1

Alcohol Use Disorder

High-Risk Inpatients (malnutrition, active withdrawal, receiving IV glucose)

Give 100-300 mg IV thiamine daily immediately, before any glucose-containing fluids. 1 Administering glucose before thiamine can precipitate acute Wernicke's encephalopathy and cause irreversible brain damage. 1

• Continue IV thiamine for 3-4 days, then transition to oral 100-300 mg daily for 2-3 months after withdrawal symptoms resolve. 1
• For patients with established Wernicke's encephalopathy, use the higher 500 mg IV three times daily regimen described above. 1

Stable Outpatients (no neurological symptoms, eating well)

Prescribe oral thiamine 100-300 mg daily for 2-3 months following any acute alcohol-related episode. 1 Standard multivitamins containing only 1-3 mg are inadequate for treatment or prevention. 1

• The IV route is preferred over oral in chronic alcohol use due to poor gastrointestinal absorption from alcohol-related gastritis. 1
• 30-80% of alcohol-dependent individuals show clinical or biological signs of thiamine deficiency. 1

Bariatric Surgery

Acute Deficiency with Prolonged Vomiting

Administer 200-300 mg thiamine daily (oral or IV if unable to tolerate oral) plus vitamin B compound strong 1-2 tablets three times daily immediately. 2, 1 Do not give oral or IV glucose to patients at risk of thiamine deficiency, as it can precipitate Wernicke-Korsakoff syndrome. 2

• Prolonged vomiting or dysphagia is not normal after bariatric surgery and should always be investigated with referral back to the bariatric center. 2
• Thiamine deficiency can develop as early as 6 weeks postoperatively in malnourished patients. 3

Prophylaxis

All bariatric surgery patients require lifelong thiamine supplementation of 50-100 mg daily due to permanent malabsorption. 1 The highest risk period is the first 3-4 months postoperatively. 1

• Standard multivitamins may be insufficient; consider additional thiamine 50 mg once or twice daily from a B-complex supplement during the high-risk period. 1
• Patients with prolonged vomiting, poor intake, or fast weight loss should receive immediate parenteral replacement of 200-300 mg daily. 1

Malnutrition and Refeeding Syndrome

Administer 300 mg IV thiamine before initiating nutrition therapy, then 200-300 mg IV daily for at least 3 more days. 1 Thiamine must be given before starting nutrition support to prevent both Wernicke's encephalopathy and refeeding syndrome. 1

• Start nutrition cautiously at 10-15 kcal/kg/day in high-risk patients and advance gradually over the first 3 days. 1
• Correct concomitant magnesium, phosphate, and potassium deficiencies before starting nutrition, as magnesium is necessary for adequate function of thiamine-dependent enzymes. 1
• Monitor electrolytes daily for the first 3-5 days and watch for clinical signs of refeeding syndrome (confusion, cardiac dysfunction, respiratory failure). 1

Prolonged Parenteral Nutrition

Standard PN formulations contain 2-6 mg thiamine daily, which prevents deficiency in most stable patients. 1 However, patients receiving high-dose glucose require higher doses of 6 mg daily. 1

• For patients with suspected deficiency or high metabolic demands (critical illness, sepsis, burns), administer 100-300 mg IV daily. 1
• Thiamine should be given before commencing PN in malnourished patients to prevent Wernicke's encephalopathy. 1

Prophylaxis in High-Risk Populations

Chronic Diuretic Therapy

Provide 50 mg oral thiamine daily due to increased renal thiamine losses. 1, 4 Approximately 6% of ambulatory heart failure patients are thiamine deficient. 1

Continuous Renal Replacement Therapy

Administer 100 mg thiamine daily due to significant losses through dialysis. 1

Critical Illness (sepsis, major trauma, burns)

Give 100-300 mg IV thiamine daily, as over 90% of critically ill patients are thiamine deficient or depleted. 1, 5

Unexplained Lactic Acidosis

Administer 100-300 mg IV thiamine immediately in any patient with unexplained lactic acidosis, particularly those with malnutrition, alcohol use disorder, or recent PN without vitamin supplementation. 1 Thiamine deficiency causes type B lactic acidosis that responds rapidly to treatment, often normalizing lactate within 24 hours. 1

Critical Timing Considerations

Always administer thiamine before glucose-containing IV fluids in any at-risk patient. 1 Glucose administration can precipitate acute Wernicke's encephalopathy in thiamine-depleted patients because thiamine is an essential cofactor for glucose metabolism. 1

• Thiamine reserves can be completely depleted within just 20 days of inadequate intake. 1
• Do not wait for laboratory confirmation to treat—thiamine deficiency can cause irreversible neurological damage or death within days to weeks if untreated. 1
• Treatment is safe with no established upper limit for toxicity; excess thiamine is excreted in urine. 1

Laboratory Assessment

Measure red blood cell or whole blood thiamine diphosphate (ThDP), not plasma thiamine, as this is the only reliable marker and is unaffected by inflammation. 1, 4 However, treatment should never be delayed while awaiting laboratory results. 4

Route Selection Algorithm

Use IV route for:

• Established or suspected Wernicke's encephalopathy 1
• Active vomiting or severe dysphagia 1
• Alcohol-related gastritis (poor absorption) 1
• Acute disease or suspected inadequate intake 1
• Patients receiving IV glucose 1
• Malabsorption syndromes 1

Use oral route for:

• Stable outpatients without neurological symptoms 1
• Maintenance therapy after IV loading 1
• Chronic prophylaxis in high-risk populations 1
• Suspected chronic deficiency without acute disease 1

Common Pitfalls to Avoid

• Never prescribe standard multivitamins (1-3 mg thiamine) for treatment or prevention in high-risk patients—this dose is grossly inadequate. 1
• Never give glucose before thiamine in at-risk patients, as this can cause irreversible brain damage. 1
• Never use low doses (10-100 mg) for patients at high risk of Wernicke's encephalopathy—this is insufficient. 1
• Never discontinue thiamine after completing IM therapy in patients with severe deficiency—tissue stores require months to fully replenish, and premature discontinuation is the most common cause of relapse. 1
• Anaphylactic reactions to parenteral thiamine are extremely rare (less than 1 in 100,000) and should not deter appropriate treatment. 6, 7