Thiamine
Vitamins
Vitamins
Vitamin B1. Given urgently in Wernicke encephalopathy and beriberi, and with IV glucose to people with low reserves, such as heavy drinkers.
Also called: vitamin B1, aneurine
Quick facts
- Group
- Vitamins
- Target
- Thiamine pyrophosphate, coenzyme of pyruvate and α-keto acid decarboxylation
- Used for
- Wernicke encephalopathy · Dry and wet beriberi
- Key effects
- Warmth · Nausea
- Monitor
- Breathing · Mental state
- ATC
- A11DA01
No doses: the clinician sets them by the current guideline.
Mechanism of action
Thiamine combines with ATP to form thiamine pyrophosphate, the coenzyme that removes carbon dioxide from pyruvate and other α-keto acids in carbohydrate metabolism. The more glucose the body burns, the more thiamine it needs. Without it, brain and heart cells cannot use glucose properly, which explains Wernicke encephalopathy and wet beriberi.
- Thiamine + ATP → thiamine pyrophosphate (TPP)
- TPP lets enzymes decarboxylate pyruvate and α-keto acids
- Glucose can feed energy production in brain and heart
Indications
- Wernicke encephalopathy (rapid replacement) Wernicke encephalopathy (thiamine deficiency) →
- Dry and wet beriberi, including infantile beriberi Beriberi (thiamine deficiency) →
- Deficiency risk in alcohol dependence, malabsorption or after bariatric surgery Alcohol use disorder →
- Neuritis of pregnancy with severe vomiting Hyperemesis gravidarum →
Adverse effects
Common
- Warmth, itching, hives, sweating
- Nausea, weakness, restlessness
- Tenderness and hardness at the IM injection site
Contraindications
- Known sensitivity to thiamine or another ingredient
Key interactions
- IV dextrose (glucose)
- In people with low thiamine reserves, glucose without thiamine can precipitate heart failure; thiamine is given alongside it
- Alcohol
- Heavy drinking is a main cause of thiamine deficiency
What is monitored
- Breathing, skin and blood pressure during and after IV injection (anaphylaxis)
- Mental state, gait and eye movements in suspected Wernicke encephalopathy
- Heart failure signs in wet beriberi
Administration and safety
- Given IM or IV; in wet beriberi with heart failure the IV injection is slow.
- If sensitivity is suspected, a small intradermal test dose is observed before the full dose.
- Airway equipment, epinephrine and oxygen are at hand.
- The injection contains aluminium: care in kidney failure and premature neonates.
Pregnancy and breastfeeding
Studies have not shown more fetal abnormalities; it is used in pregnancy when clearly needed, for example with severe vomiting.
Nursing care
- In a patient who drinks heavily or is malnourished, make sure thiamine is given with IV glucose as ordered.
- Watch for anaphylaxis after each injection, especially repeated ones.
- Ask about alcohol use, malabsorption, dialysis and bariatric surgery.
Pharmacokinetics
- Absorption
- Rapid and complete after intramuscular injection
- Distribution
- Reaches all tissues, highest in liver, brain, kidney and heart
- Metabolism
- Rapidly metabolised
- Elimination
- Excess leaves in the urine, unchanged once tissues are saturated
Test yourself
Think of the answer, then tap the question to see it.
Which coenzyme does thiamine form, and what reaction does it allow?
Thiamine pyrophosphate, which decarboxylates pyruvate and other α-keto acids.
Why is thiamine given with IV glucose in a malnourished heavy drinker?
Glucose increases thiamine demand; without thiamine it can precipitate heart failure.
What is the most serious adverse reaction of injected thiamine?
Anaphylaxis, sometimes fatal, especially after repeated doses.
What separates wet from dry beriberi?
Wet beriberi affects the heart (heart failure); dry beriberi affects the nerves.
Connections
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - THIAMINE HYDROCHLORIDE INJECTION, SOLUTION injection, solution (DailyMed (U.S. National Library of Medicine), 2026); Thiamine (Vitamin B1) : MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.