Bedside Snapshot

Use It For: Suspected Wernicke encephalopathy; prevention in alcohol withdrawal, malnutrition or prolonged vomiting; refeeding-syndrome risk; wet beriberi or thiamine-deficiency lactic acidosis
Adult Dose: Suspected Wernicke: 500 mg IV every 8 hr for at least 3 days
Prevention: 100 mg IV/IM daily for 3–5 days
Refeeding risk: 100 mg before feeding, then daily for 5–7 days
Pediatric Dose: Refeeding risk: 2 mg/kg/day IV or PO (max 100–200 mg/day); infant beriberi with collapse: 25–50 mg slow IV. Suspected Wernicke: no evidence-based dose; specialist-guided dosing
Onset / Duration: IV: clinical response within hours–days (eye signs, heart failure, lactate); neurologic recovery can take weeks and may be incomplete
Do Not Give / Hold If: Known hypersensitivity to thiamine or a product ingredient. No other hold parameters: do not withhold in suspected deficiency
Watch For: Anaphylaxis (rare; hives, throat tightness, hypotension), more likely after repeated injections; IM site pain; no neurologic response after 72 hr (check Mg²⁺)
Reversal / Rescue: No reversal needed. Anaphylaxis: stop the dose, IM epinephrine, oxygen and airway support per protocol
Must Remember: Never delay dextrose to give thiamine first: give them in any order or together. Wernicke treatment (500 mg every 8 hr, 1,500 mg/day) is 5 times the prevention dose per dose and 15 times per day

Indications

Emergency & Prehospital

Suspected Wernicke encephalopathy (WE): in alcohol use disorder, EFNS needs any two of dietary deficiency, eye signs, cerebellar dysfunction (ataxia), or altered mental state or mild memory impairment. In other at-risk patients (hyperemesis, bariatric surgery, malnutrition, prolonged vomiting), any condition that can cause thiamine deficiency is a reason to suspect WE. Treat on suspicion. Don't sit and wait for the full triad.
Altered or intoxicated patient at risk of thiamine deficiency: the risk comes from alcohol use disorder, malnutrition or prolonged vomiting. EFNS advises parenteral thiamine for every at-risk ED patient. When hypoglycemia is treated, give thiamine alongside dextrose.
Alcohol withdrawal: every patient treated for withdrawal gets thiamine to prevent WE, given together with benzodiazepines or phenobarbital.

ED / ICU / Transport

Refeeding syndrome risk: starved, malnourished or chronically drinking patients. Give it before nutrition or dextrose-containing IV fluids start.
Wet beriberi: thiamine deficiency can cause high-output heart failure, including the fulminant shoshin form with shock and lactic acidosis. The label treats it as an emergency cardiac indication.
Unexplained lactic acidosis in a high-risk patient: think thiamine in patients with alcohol use disorder, malnutrition, bariatric surgery or thiamine-deficient parenteral nutrition.
Infantile beriberi with collapse: the infant shows heart failure, respiratory distress, encephalopathy or severe lactic acidosis. The usual case is a breastfed infant of a thiamine-deficient mother.
Hyperemesis gravidarum and other prolonged vomiting: the label lists neuritis of pregnancy with severe vomiting, and established deficiency when severe vomiting prevents taking oral thiamine. Hyperemesis gravidarum is a recognized cause of WE.

Other Uses

Established deficiency with malabsorption, anorexia or vomiting: when oral intake is not possible, replace it parenterally.
After bariatric surgery: the risk is ongoing. Follow thiamine status for at least 6 months (EFNS). Give parenteral thiamine for vomiting, poor intake or any sign of deficiency.
Not a sepsis therapy: routine thiamine, with vitamin C and hydrocortisone, did not improve outcomes in sepsis. Give it only when deficiency is suspected.

Dosing & Administration

This page departs from the FDA label. The label gives 10–20 mg IM three times daily, for as long as two weeks, for beriberi. This page uses 100–200 mg slow IV once daily for wet beriberi. That dose rests on Smith 2021 case reports and is protocol-dependent. For infant collapse it uses 25–50 mg slow IV, where the label says 25 mg.

Available Forms

Injection: 100 mg/mL in a 2 mL (200 mg) multiple-dose vial, for IV or IM use. 100 mg is 1 mL. This is the form EMS and EDs carry. It also contains chlorobutanol 0.5% (a chloral derivative, used as a preservative) and monothioglycerol 0.5%. The label warns that it contains aluminum, which may reach toxic levels with prolonged parenteral use in renal impairment or premature neonates.
Tablets: oral thiamine for maintenance and low-risk prevention. Strengths vary by manufacturer.
Multivitamin products: they carry small amounts of thiamine. That is enough for maintenance and not enough to treat WE.

Adult Dosing

Indication	Dose & Route	Repeat / Max	Notes
Suspected or confirmed Wernicke encephalopathy	500 mg IV every 8 hr, diluted and infused	For at least 3 days; usual ceiling 500 mg/dose (1,500 mg/day)	EFNS 2010 recommends 200 mg three times daily, preferably IV; ASAM 2020 ICU discussion text cites 200–500 mg IV every 8 hr. No dose has proven superior in trials, so regimens vary by protocol. Then continue 100 mg or more daily (IV/IM, then PO) until eating a normal diet. Correct magnesium.
Prevention: alcohol withdrawal, malnutrition, high-risk ED patient	100 mg IV/IM once daily	Typical: 3–5 days. No defined max: some protocols use higher prophylactic doses	ASAM 2020 typical dose; IV or IM preferred with poor nutrition, malabsorption or complicated withdrawal. A prevention RCT found no difference between 100 mg daily and 100 or 300 mg three times daily. ICU patients whose illness masks or mimics WE: use the WE row.
Mild withdrawal, low risk, able to eat	100 mg PO once daily	Typical: 3–5 days. No defined max	Oral absorption is limited and further reduced by alcohol: switch to IV/IM if any WE sign appears.
Refeeding syndrome risk, including prolonged vomiting with poor intake	100 mg IV or PO before feeding or dextrose-containing IV fluids	Then 100 mg daily for 5–7 days or longer. No defined max	ASPEN 2020. Use the WE row if neurologic signs are present. Check K⁺, Mg²⁺ and phosphate before feeding.
Hyperemesis gravidarum (admitted with vomiting or severely reduced intake)	100 mg PO three times daily; give IV/IM instead if vomiting prevents reliable oral intake	No defined max; continue while intake is poor. Parenteral dose and duration per protocol	RCOG 2024 (UK) gives thiamine to every woman admitted with vomiting or severely reduced intake, especially before dextrose or parenteral nutrition; its IV option is a vitamin B complex product. ASPEN has no hyperemesis-specific dose. Use the WE row if any neurologic sign appears.
Wet beriberi or thiamine-deficiency lactic acidosis	100–200 mg slow IV once daily	No fixed max: escalate to the WE row if encephalopathy coexists	Label: treat wet beriberi with heart failure as a cardiac emergency and give thiamine slowly IV. Expect improvement over hours to days.

Pediatric Dosing

Indication	Dose (per kg) & Route	Max Single / Max Total	Notes
Refeeding syndrome risk (high-risk child)	2 mg/kg IV or PO before feeding or dextrose-containing IV fluids	Max 100–200 mg/day; continue daily for 5–7 days or longer	ASPEN 2020 pediatric recommendation; ASPEN specifies no dosing weight.
Infantile beriberi with collapse (heart failure, lactic acidosis, encephalopathy)	25–50 mg slow IV immediately (label: 25 mg cautiously IV)	Fixed dose, not per kg; then daily IV/IM dosing per specialist	WHO 1999 regimen: 25–50 mg IV, then 10 mg IM daily for 10 days, then oral. WHO Western Pacific 2017: 25 mg IV plus 25 mg IM, then 25 mg daily until the child can eat. Published infant series mostly gave 100 mg IV or IM (range 50–300 mg/day). Treat the breastfeeding mother too.
Suspected Wernicke encephalopathy	No evidence-based pediatric dose. Give IV thiamine without delay; dose set by a specialist	No defined max: specialist-guided	Consult pediatric critical care or neurology for ongoing dosing.

See weight-based dosing for pediatric calculation checks.

Preparation & Administration

Push rate: give slowly. A 100 mg dose can go in by slow IV push. In a prospective series of 989 patients, 1,070 doses of 100 mg IV push caused a reaction in 12 (1.1%). Of those, 11 were transient local irritation and 1 was generalized pruritus.
Dilution: dilute high doses (200–500 mg) in normal saline and infuse them rather than push. Saline is the preferred diluent. Volume and rate follow institutional practice.
IM: use it when there is no IV access. The shot can cause tenderness and induration, so avoid repeated IM doses when IV is available.
Stability: neutral or alkaline solutions destroy thiamine fast. Don't mix it with sodium bicarbonate or other alkaline drugs.
Light: keep vials in the carton until use. Use only a clear solution.

Contraindications & Precautions

Contraindications

Hypersensitivity: a history of sensitivity to thiamine or any product ingredient. The label names this as the only contraindication.

Precautions

Suspected sensitivity: for anyone with a drug allergy history or a prior reaction to thiamine, the label advises an intradermal test first: one-hundredth of the dose, with 30 min of observation. A positive test means no injectable thiamine. After a negative test, give the full dose and observe for at least 30 min. A negative test still doesn't rule out a reaction.
Repeated injections: the risk of serious hypersensitivity and anaphylaxis is higher after repeated IV or IM doses. Deaths have been reported.
Renal impairment, including premature neonates: the injection contains aluminum. When kidney function is impaired, parenteral aluminum above 4–5 mcg/kg/day builds up to levels linked with CNS and bone toxicity. Tissue loading can happen at lower rates.
Multiple deficiencies: isolated thiamine deficiency is rare. Check magnesium, phosphate, potassium and folate in the same patient.

Hold / Reassess If

Urticaria, throat tightness, wheeze, angioedema or hypotension during or after a dose: stop and treat as anaphylaxis
No neurologic improvement after 72 hr of high-dose therapy: check magnesium and reconsider the diagnosis

Never delay dextrose for thiamine: a hypoglycemic patient gets dextrose now. EFNS 2010 puts thiamine ahead of any carbohydrate. ASAM 2020 found no clinical evidence that glucose first triggers WE, so it accepts either order, or both at once. Whatever the order, hypoglycemia is never left untreated while thiamine is pending.

Adverse Effects & Toxicity

Common

Injection-site reactions: tenderness and induration are the usual reactions after IM injection. IV push can cause transient local irritation, about 1% of 100 mg IV doses.
Feeling of warmth, pruritus, sweating, nausea, restlessness: reported, uncommon

Serious / Life-Threatening

Anaphylaxis: rare, but it can be fatal, especially after repeated injections. Watch for urticaria, angioedema, throat tightness, cyanosis and collapse. Stop the drug, then give IM epinephrine, oxygen and airway support per anaphylaxis protocol.
Other reported reactions: pulmonary edema and gastrointestinal hemorrhage. The label lists both as rare.

Overdose & Toxicity Management

Toxicity: single parenteral doses of 100–500 mg have been given with no toxic effects. The excess leaves the body in urine.
Management: no antidote is needed. Treat any hypersensitivity reaction supportively.

Monitoring

Parameter	When / How Often	Target / Act If
Clinical: mental status, eye movements, gait	Baseline, then at least daily during the IV course	No improvement after 72 hr of high-dose thiamine: check Mg²⁺, reconsider the diagnosis, MRI and neurology review
Clinical: hypersensitivity	During and for 30 min after each injection, especially repeat courses	Hives, wheeze, throat tightness or hypotension: stop, treat as anaphylaxis
Laboratory: glucose	Point-of-care glucose in every altered patient before or with the first dose	Low glucose: give dextrose immediately; do not wait for thiamine
Laboratory: magnesium	Baseline in alcohol use disorder, malnutrition or refeeding	Low Mg²⁺ impairs thiamine use: replace with IV magnesium
Laboratory: K⁺, Mg²⁺, phosphate (refeeding)	Before feeding, then every 12 hr for the first 3 days in high-risk patients	Falling K⁺, Mg²⁺ or phosphate: replace; severely low or dropping fast: cut calories by 50%
Laboratory: lactate	Baseline and repeat in suspected wet beriberi or unexplained lactic acidosis	Rapid fall in lactate after thiamine supports deficiency; persistent rise: look for another cause
Laboratory: thiamine level	Optional: draw before the first dose only if it causes no delay	Never wait for a result; ASPEN 2020: routine levels are unlikely to be of value

Interactions & Compatibility

Clinically Significant Interactions

Drug / Class	Effect	What To Do
Dextrose and other carbohydrate loads	Raise thiamine demand; can unmask deficiency in depleted patients	Give in any order or together (thiamine first only when it causes no delay); never delay dextrose for hypoglycemia
Alcohol (ethanol)	Reduces intestinal thiamine absorption and impairs its conversion to the active form	Use IV or IM rather than PO in active drinkers and in withdrawal
Magnesium deficiency	Magnesium is a cofactor for thiamine activation and thiamine-dependent enzymes	Check and replace Mg²⁺ when WE does not respond
Alkaline drugs and solutions (e.g. sodium bicarbonate)	Rapid destruction of thiamine in neutral or alkaline solution	Do not mix in the same syringe or bag; flush between drugs

IV Compatibility

Preferred diluent: 0.9% sodium chloride (normal saline).
Dextrose fluids: when dextrose goes to a patient with marginal thiamine status, the label allows 100 mg in each of the first few liters of IV fluid.
Incompatible: neutral or alkaline solutions.
Verify with an institutional compatibility resource.

Special Populations

Pediatrics: no evidence-based pediatric treatment recommendations exist, so doses are empirical. A symptomatic infant needs thiamine given directly, because supplementing the mother does not correct the infant quickly. Start with the Pediatric Dosing table.
Neonates: the injection contains aluminum. Premature neonates are at particular risk, because their kidneys are immature. The label’s 4–5 mcg/kg/day accumulation threshold applies to every patient with impaired kidney function. Tissue loading can happen at lower rates.
Pregnancy: studies in pregnant women have not shown a higher risk of fetal abnormalities, and fetal harm looks remote. Hyperemesis gravidarum can cause WE. Treat suspected deficiency promptly and fully.
Lactation: the label lists excretion in milk as unknown. Thiamine is a normal part of breast milk, and maternal supplementation raises milk levels. When deficiency is suspected, the benefit outweighs the risk.
Older Adults: no specific adjustment has been established.
Renal Impairment: no dose adjustment has been established. Long parenteral courses can build up aluminum.
Hepatic Impairment: no dose adjustment has been established. Liver disease often coexists with alcohol-related deficiency.
Obesity / Dosing Weight: adult doses are fixed, not weight-based. ASPEN gives no dosing weight for the pediatric 2 mg/kg refeeding dose. The 100–200 mg/day cap still applies.
Long-Term Loop-Diuretic Therapy: small heart failure studies link long-term furosemide to more urinary thiamine loss and biochemical thiamine deficiency. When other risks coexist, consider deficiency in these patients.
After Bariatric Surgery: the risk of deficiency is ongoing, and it peaks with vomiting or poor intake. Follow thiamine status for at least 6 months (EFNS). Keep up the prescribed thiamine-containing supplement, and give parenteral thiamine for vomiting, poor intake or any sign of deficiency.

Field & Transport Considerations

Scope: paramedic and critical-care services commonly carry it for altered patients with alcohol use disorder or malnutrition (Paramedic/RN/CCT). It varies by state and agency protocol.
Storage & Stability: store at 20–25°C (68–77°F). Protect it from light in the carton. Avoid prolonged heat in the vehicle. Discard a cloudy solution.
Carried Concentration: 100 mg/mL, in a 2 mL multiple-dose vial. 100 mg is 1 mL, so the whole vial holds 200 mg. Follow agency policy for multiple-dose vials.
Glucose First: check glucose in every altered patient. Treat hypoglycemia with dextrose now. Don't wait on thiamine, or on IV access for thiamine.
Interfacility Transport: check whether the patient is on a prevention schedule (100 mg daily) or a WE treatment schedule (every 8 hr). Then confirm when the next dose is due.
Handoff Essentials: dose, route and time of thiamine; dextrose given and glucose values; mental status, eye findings and gait; alcohol history and last drink; magnesium if known.

Clinical Pearls

Do not wait for the triad: in alcohol use disorder, two of four findings is enough under EFNS criteria. Those four are dietary deficiency, eye signs, cerebellar signs, and altered mental state or mild memory impairment. In other at-risk patients, suspect WE whenever deficiency is possible. Left untreated, WE can progress to Korsakoff syndrome, with memory loss that lasts.

Prevention dose is not treatment: 100 mg once daily protects at-risk patients from WE, but it undertreats WE that is already here. Any WE sign means high-dose IV thiamine every 8 hr.

Exam discriminator: thiamine before dextrose? Older teaching, and EFNS 2010, put thiamine first. ASAM 2020 found no evidence for that, and it allows any order or both together. With a hypoglycemic patient, dextrose is the priority. Thiamine follows right behind it.

A banana bag is not WE treatment: the multivitamin “banana bag” does not treat it. The ASAM 2020 discussion cites evidence-based recommendations for 200–500 mg IV thiamine every 8 hr, magnesium sulfate 64 mg/kg and folate 400–1,000 mcg IV in its place. The recommendation covers ICU patients whose illness masks or mimics WE.

Thiamine-refractory? Check magnesium: thiamine needs magnesium to be activated. Low Mg²⁺ can blunt the response, so replace it.

Lactic acidosis that melts away: think shoshin beriberi when you see high-output shock with severe lactic acidosis. Then watch the lactate after thiamine. In malnourished, alcohol-using or post-bariatric patients, a lactate that falls within hours supports the diagnosis.

Not a sepsis drug: the VICTAS trial tested routine vitamin C, thiamine and hydrocortisone. It did not improve ventilator- and vasopressor-free days. Give thiamine to septic patients only when deficiency is suspected.

Pharmacology

Mechanism of Action

Thiamine becomes thiamine pyrophosphate (thiamine diphosphate, TDP), a coenzyme. Activation needs ATP and magnesium.
TDP runs pyruvate dehydrogenase, α-ketoglutarate dehydrogenase and transketolase. Those enzymes link glycolysis to the Krebs cycle and the pentose phosphate pathway.
Deficiency means pyruvate and lactate build up, and ATP falls in high-demand tissue. The damage shows up as WE (brain), wet beriberi (heart) or neuropathy (dry beriberi).
Carbohydrate loads raise the thiamine requirement. That is why refeeding can unmask deficiency.

Pharmacokinetics

Route	Onset	Peak	Duration
IV	Clinical response within hours–days	—	Short; repeat dosing
IM	Absorption rapid and complete	—	Same as IV
PO	Absorption limited; reduced by alcohol	—	Maintenance only

Half-life: short. Metabolism is rapid, and the excess goes out in urine. That is why treatment regimens repeat doses every 8 hr.
Distribution and stores: it reaches all tissues, with the highest levels in liver, brain, kidney and heart. Stores are limited and run out after about 3 weeks without intake.
Metabolism: tissues phosphorylate it to TDP. Any excess is metabolized and excreted.
Elimination: urine. Once tissues are saturated, it leaves as pyrimidine, and at higher doses it leaves unchanged.

Names & Classification

Generic Name: Thiamine hydrochloride (vitamin B1)
Brand Names: Generic only in the US (multiple manufacturers); also a component of multivitamin products
Pharmacologic Class: Water-soluble vitamin (B1); coenzyme precursor
Therapeutic Class: Nutritional replacement; treatment and prevention of Wernicke encephalopathy and beriberi
Controlled Substance: Not controlled
ISMP High-Alert: No
Look-Alike / Sound-Alike: Check the current ISMP confused drug names list; read the mg dose aloud, because WE treatment (500 mg every 8 hr) is 5 times the prevention dose per dose and 15 times per day

References

Sagent Pharmaceuticals. (2025). Thiamine hydrochloride injection, USP, 100 mg/mL [prescribing information] (revised June 2025). DailyMed, National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=5982cf83-01d6-4acb-8373-339079b8a76e
American Society of Addiction Medicine. (2020). The ASAM clinical practice guideline on alcohol withdrawal management. Journal of Addiction Medicine, 14(3S Suppl 1), 1–72. https://www.asam.org/docs/default-source/quality-science/the_asam_clinical_practice_guideline_on_alcohol-1.pdf
da Silva, J. S. V., Seres, D. S., Sabino, K., Adams, S. C., Berdahl, G. J., Citty, S. W., ... Ayers, P. (2020). ASPEN consensus recommendations for refeeding syndrome. Nutrition in Clinical Practice, 35(2), 178–195. https://doi.org/10.1002/ncp.10474 (Erratum: Nutrition in Clinical Practice, 35(3), 584–585.)
Galvin, R., Bråthen, G., Ivashynka, A., Hillbom, M., Tanasescu, R., & Leone, M. A. (2010). EFNS guidelines for diagnosis, therapy and prevention of Wernicke encephalopathy. European Journal of Neurology, 17(12), 1408–1418. https://doi.org/10.1111/j.1468-1331.2010.03153.x
Smith, T. J., Johnson, C. R., Koshy, R., Hess, S. Y., Qureshi, U. A., Mynak, M. L., & Fischer, P. R. (2021). Thiamine deficiency disorders: a clinical perspective. Annals of the New York Academy of Sciences, 1498(1), 9–28. https://doi.org/10.1111/nyas.14536
Smith, H., McCoy, M., Varughese, K., & Reinert, J. P. (2021). Thiamine dosing for the treatment of alcohol-induced Wernicke’s encephalopathy: a review of the literature. Journal of Pharmacy Technology, 37(2), 107–113. https://doi.org/10.1177/8755122520962859
Dingwall, K. M., Delima, J. F., Binks, P., Batey, R., & Bowden, S. C. (2022). What is the optimum thiamine dose to treat or prevent Wernicke’s encephalopathy or Wernicke–Korsakoff syndrome? Results of a randomized controlled trial. Alcoholism: Clinical and Experimental Research, 46(6), 1133–1147. https://doi.org/10.1111/acer.14843
Sevransky, J. E., Rothman, R. E., Hager, D. N., Bernard, G. R., Brown, S. M., Buchman, T. G., ... Martin, G. S. (2021). Effect of vitamin C, thiamine, and hydrocortisone on ventilator- and vasopressor-free days in patients with sepsis: the VICTAS randomized clinical trial. JAMA, 325(8), 742–750. https://doi.org/10.1001/jama.2020.24505
Nelson-Piercy, C., et al. (2024). The management of nausea and vomiting in pregnancy and hyperemesis gravidarum (Green-top Guideline No. 69). BJOG, 131(7), e1–e30. https://doi.org/10.1111/1471-0528.17739
Wrenn, K. D., Murphy, F., & Slovis, C. M. (1989). A toxicity study of parenteral thiamine hydrochloride. Annals of Emergency Medicine, 18(8), 867–870. https://doi.org/10.1016/s0196-0644(89)80215-x
Seligmann, H., Halkin, H., Rauchfleisch, S., Kaufmann, N., Motro, M., Vered, Z., & Ezra, D. (1991). Thiamine deficiency in patients with congestive heart failure receiving long-term furosemide therapy: a pilot study. American Journal of Medicine, 91(2), 151–155. https://doi.org/10.1016/0002-9343(91)90007-k
Shimon, I., Almog, S., Vered, Z., Seligmann, H., Shefi, M., Peleg, E., Rosenthal, T., Motro, M., Halkin, H., & Ezra, D. (1995). Improved left ventricular function after thiamine supplementation in patients with congestive heart failure receiving long-term furosemide therapy. American Journal of Medicine, 98(5), 485–490. https://doi.org/10.1016/s0002-9343(99)80349-0

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Thiamine (Vitamin B1)