Vitamin
Thiamine
Indications
- Suspected or confirmed Wernicke encephalopathy: high-dose IV on suspicion
- Prophylaxis, before or with glucose, in alcohol use disorder, malnutrition, hyperemesis or after bariatric surgery
- Refeeding syndrome prevention, before feeding starts
- Wet and Shoshin beriberi: high-output heart failure with lactic acidosis
- Unexplained type B lactic acidosis in at-risk patients (off-label)
- Ethylene glycol poisoning, to steer glyoxylate away from oxalate (off-label)
Dosing
| Where | Dose |
|---|---|
| Metabolic and electrolyte boluses | Thiamine: 100–500 mg IV before or with glucose in suspected deficiency |
Mechanism of action
Thiamine enters cells on carriers (THTR-1 and THTR-2), and thiamine pyrophosphokinase converts it to thiamine pyrophosphate (TPP), the coenzyme for pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, branched-chain keto acid dehydrogenase and transketolase in the pentose phosphate pathway. Without TPP, pyruvate backs up into lactate, ATP falls and neurons in high-demand areas (mammillary bodies, medial thalamus, periaqueductal gray, cerebellar vermis) swell and die. A glucose load pushes more flux through these enzymes and uses up the last TPP, so thiamine goes before or with glucose in anyone at risk.
Pharmacology
- CNS: eye signs often improve within hours to days, ataxia and confusion over days to weeks; Korsakoff amnesia often persists
- Cardiovascular: corrects the vasodilation and high-output failure of wet beriberi, sometimes within hours
- Metabolic: lowers lactate only when deficiency drives it (in septic shock, only in the 35% who were deficient)
- Neuromuscular: dry beriberi neuropathy improves over months
Pharmacokinetics
| Onset | IV: immediate; clinical response in hours to days, eye signs first |
|---|---|
| Half-life | Plasma about 1.5 h (96 min after 50 mg IV, Tallaksen 1993); body pool 9–18 days |
| Distribution | Highest in liver, heart, kidney and brain (label); body content 25–30 mg, about 80% as TPP |
| Protein binding | Loose, mainly albumin |
| Metabolism | Phosphorylated in cells to TPP; about 1 mg a day is degraded, mainly to pyrimidine and thiazole fragments |
| Elimination | Urine: little at normal intake; large doses spill unchanged (53% of a 50 mg IV dose in 24 h) |
| Dialysis | Removed by hemodialysis and CRRT; long CRRT can cause deficiency |
| Bioavailability | Oral about 5% of a 50 mg dose; carrier-limited and impaired by alcohol, so give IV for Wernicke |
Chemistry
- An aminopyrimidine joined by a methylene bridge to a thiazolium ring, whose C2 carbon forms the carbanion that attacks α-keto acids
- The thiazolium nitrogen is permanently charged and the aminopyrimidine pKa is about 4.8, so at pH 7.4 it is a water-soluble cation that needs carriers to cross membranes
- Injection 100 mg/mL (2 mL multiple-dose vials with chlorobutanol), pH 2.5–4.5; protect from light. Destroyed quickly in neutral or alkaline solutions (not with bicarbonate) and by sulfites
Adverse effects and cautions
In the one-pagers
- Toxidromes and AntidotesThe first hour: approach to the poisoned patient: Stabilize first, identify second. Support airway and breathing, check a fingerstick glucose in anyone with altered mental status, and titrate naloxone to breathing, not full arousal. Give thiamine 100 mg IV with dextrose to malnourished or alcohol-dependent patients (Merck). Start continuous ECG and SpO₂, get a 12-lead, measure core temperature and
- Electrolyte ImbalancesMagnesium, phosphate and refeeding: Thiamine 100 mg before feeding or dextrose, then daily for 5–7 days in high risk.
- ABG Interpretation in 6 StepsCauses in depth: High-gap acidosis: MUDPILES is the classic list (methanol, uremia, DKA, propylene glycol, isoniazid and iron, lactate, ethylene glycol, salicylates). GOLDMARK (Mehta 2008) fits the ICU better: glycols, 5-oxoproline (regular acetaminophen in malnourished or septic patients), L-lactate, D-lactate (short bowel), methanol, aspirin, renal failure and ketoacidosis (diabetic, alcoholic,
- Shock Types at a GlanceOxygen delivery, consumption and lactate: Type B1: Underlying disease: Liver failure, malignancy, thiamine deficiency
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Sources
- FDA label: thiamine HCl injection, Fresenius Kabi (2019)
- Tallaksen 1993 (kinetics)
- Wrenn 1989 (IV safety)
- Harper 1986 (Wernicke autopsy series)
For education and exam preparation only. Follow your institution’s protocols. Typical adult values for study. Follow your local protocols and medical direction.