๐ Thiamine (Vitamin Bโ) is an essential water-soluble vitamin required for carbohydrate metabolism and neural function.
Deficiency is classically associated with Wernickeโs encephalopathy and beriberi.
In patients at risk of malnutrition (especially alcohol misuse), parenteral replacement with Pabrinexยฎ should be given before any carbohydrate or glucose load to prevent precipitation of acute Wernickeโs.
๐ About
- Always check the BNF entry here for up-to-date prescribing information.
- Thiamine is a cofactor for several key enzymes in glucose metabolism โ deficiency leads to impaired ATP generation and selective neuronal injury.
- Alcohol dependence, poor diet, or malabsorption are the main risk factors for deficiency.
โ๏ธ Mode of Action
- Acts as an essential coenzyme (in the form of thiamine pyrophosphate) for:
- Pyruvate dehydrogenase (link between glycolysis and Krebs cycle)
- ฮฑ-ketoglutarate dehydrogenase (Krebs cycle)
- Transketolase (pentose phosphate pathway)
- Deficiency โ reduced oxidative metabolism โ accumulation of lactate โ neuronal energy failure and cerebral oedema (Wernickeโs).
๐ Indications & Doses
- Mild deficiency: Thiamine 25โ100 mg daily PO.
- Moderate to severe deficiency: Thiamine 200โ300 mg daily PO.
- Wernickeโs encephalopathy / risk with alcohol misuse:
- Pabrinexยฎ IV High Potency: 2โ3 pairs of ampoules three times daily for 2โ3 days (each 5 mL vial contains 250 mg thiamine + 4 mg riboflavin + 160 mg nicotinamide).
- Thiamine 400-500 mg IV TDS for 3 days and then review. Continue thiamine 400 mg IV three times daily on day 4 and 5 if indicated or switch to oral thiamine if appropriate. From day 6 give oral thiamine if appropriate or give thiamine 400 mg IV once daily until cognition plateaus, with daily review.
- Ensure magnesium is monitored, and corrected if necessary, during thiamine treatment
- Long term: oral thiamine 100 mg TDS once clinically stable.
๐ Interactions
- Clinically significant interactions are rare.
- See BNF for updates.
โ ๏ธ Cautions
- Use IV Pabrinexยฎ with caution in patients with history of allergy โ anaphylaxis is rare but reported.
- Administer slowly over โฅ10 minutes with resuscitation facilities available.
- Monitor magnesium concurrent deficiency impairs thiamine utilisation.
๐ซ Contraindications
- Known hypersensitivity to thiamine or other Pabrinexยฎ components.
๐ฅ Adverse Effects
- Generally well tolerated orally.
- Rare: anaphylactic or anaphylactoid reactions with IV Pabrinexยฎ.
- Local irritation or thrombophlebitis at injection site (uncommon).
๐ง Teaching Note
Thiamine deficiency is a preventable cause of acute neurological catastrophe.
Always give parenteral thiamine before IV glucose in at-risk patients โ glucose administration can precipitate Wernickeโs by exhausting residual thiamine stores.
The triad of confusion, ophthalmoplegia, and ataxia should prompt immediate IV Pabrinexยฎ administration.
๐ References
- BNF: Thiamine
- Royal College of Physicians: Guidelines on Wernickeโs Encephalopathy (2023)
- NICE NG64: Alcohol-use disorders โ diagnosis and management of physical complications
