Makindo Medical Notes

💊 Thiamine (Vitamin B₁) is an essential water-soluble vitamin required for carbohydrate metabolism and neural function. Deficiency is classically associated with Wernicke’s encephalopathy and beriberi. In patients at risk of malnutrition (especially alcohol misuse), parenteral replacement with Pabrinex® should be given before any carbohydrate or glucose load to prevent precipitation of acute Wernicke’s.

📘 About

• Always check the BNF entry here for up-to-date prescribing information.
• Thiamine is a cofactor for several key enzymes in glucose metabolism — deficiency leads to impaired ATP generation and selective neuronal injury.
• Alcohol dependence, poor diet, or malabsorption are the main risk factors for deficiency.

⚙️ Mode of Action

• Acts as an essential coenzyme (in the form of thiamine pyrophosphate) for:
  • Pyruvate dehydrogenase (link between glycolysis and Krebs cycle)
  • α-ketoglutarate dehydrogenase (Krebs cycle)
  • Transketolase (pentose phosphate pathway)
• Deficiency → reduced oxidative metabolism → accumulation of lactate → neuronal energy failure and cerebral oedema (Wernicke’s).

💊 Indications & Doses

• Mild deficiency: Thiamine 25–100 mg daily PO.
• Moderate to severe deficiency: Thiamine 200–300 mg daily PO.
• Wernicke’s encephalopathy / risk with alcohol misuse:
  • Pabrinex® IV High Potency: 2–3 pairs of ampoules three times daily for 2–3 days (each 5 mL vial contains 250 mg thiamine + 4 mg riboflavin + 160 mg nicotinamide).
  • Follow with oral thiamine 100 mg TDS once clinically stable.

🔄 Interactions

• Clinically significant interactions are rare.
• See BNF for updates.

⚠️ Cautions

• Use IV Pabrinex® with caution in patients with history of allergy — anaphylaxis is rare but reported.
• Administer slowly over ≥10 minutes with resuscitation facilities available.
• Monitor magnesium — concurrent deficiency impairs thiamine utilisation.

🚫 Contraindications

• Known hypersensitivity to thiamine or other Pabrinex® components.

💥 Adverse Effects

• Generally well tolerated orally.
• Rare: anaphylactic or anaphylactoid reactions with IV Pabrinex®.
• Local irritation or thrombophlebitis at injection site (uncommon).

🧠 Teaching Note

Thiamine deficiency is a preventable cause of acute neurological catastrophe. Always give parenteral thiamine before IV glucose in at-risk patients — glucose administration can precipitate Wernicke’s by exhausting residual thiamine stores. The triad of confusion, ophthalmoplegia, and ataxia should prompt immediate IV Pabrinex® administration.

📚 References

• BNF: Thiamine
• Royal College of Physicians: Guidelines on Wernicke’s Encephalopathy (2023)
• NICE NG64: Alcohol-use disorders — diagnosis and management of physical complications