Section 18 · Monograph
Thiamine
Reviewed Nov 2026FDA label
Vitamin B1Vitamin (cofactor)
- Forms
- Inj: 100mg/mL | Tab: 50, 100mg
- Dose
- Wernicke's encephalopathy: 500mg IV TID for 2-3 days, then 250mg IV daily for 3-5 days; give before glucose
- MOA
- Cofactor for carbohydrate metabolism enzymes
Indications
- Thiamine deficiency (beriberi)FDA-labeled
- Treatment and prophylaxis of Wernicke's encephalopathy in at-risk patients (alcohol use disorder, malnutrition)FDA-labeled
Mechanism of Action
- Precursor of thiamine pyrophosphate, a cofactor for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase and transketolase essential for neuronal energy metabolism
Full Dosing
Adult / usual
- Wernicke's encephalopathy: 500mg IV three times daily for 2-3 days, then 250mg IV daily for 3-5 days, then oral 100mg daily
- Give before or with glucose-containing fluids in at-risk patients
- Prophylaxis in at-risk patients: 100-250mg IV or IM daily
Contraindications
- Known hypersensitivity (rare anaphylaxis with parenteral use)
Drug Interactions
- May potentiate neuromuscular blocking agents
- Loop diuretics and chronic phenytoin may lower thiamine levels
Adverse Effects
- Rare anaphylaxis or hypersensitivity with IV use — give slowly
- Injection-site pain
- Hypotension if injected rapidly
Monitoring Parameters
- Neurologic status (ophthalmoplegia, ataxia, confusion)
- Nutritional status; replete magnesium
Pregnancy & Lactation
- Safe at recommended doses; requirements are increased in pregnancy
- Compatible with breastfeeding