Vitamin B1 Pregnancy: This product is not intended for use in pregnant or lactating women.

Thiamine

Brand names: Pabrinex (combo)

Thiamine (vitamin B1) is a water-soluble vitamin used to prevent and treat deficiency states, including Wernicke's encephalopathy and deficiency related to chronic alcohol use or malnutrition.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Mild chronic deficiency: 50 mg daily. Severe deficiency: 100 mg three times daily

Route: Oral

Frequency: Once daily (mild deficiency) or three times daily (severe deficiency)

Product: thiamine hydrochloride 100 mg tablets. Dosing applies to adults, the elderly and children over three years of age. Not recommended for children under three years.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to thiamine hydrochloride or to any excipient

Side effects

Mild gastrointestinal events - nausea, vomiting, diarrhoea, abdominal pain (frequency not known)
Hypersensitivity reactions, mainly after parenteral administration
Allergic and anaphylactic reactions - pruritus, urticaria, angioedema, respiratory distress, tachycardia, palpitations, shock (frequency not known)

Interactions

Thiamine antagonists thiosemicarbazone and 5-fluorouracil can neutralise the effect of thiamine - dose may need adjusting
May give false positive urobilinogen results by Ehrlich's reaction
High doses may interfere with spectrophotometric assays of theophylline plasma concentration

Clinical monograph

How it works

As the cofactor thiamine pyrophosphate, it is essential for carbohydrate metabolism, supporting enzymes such as transketolase and pyruvate and alpha-ketoglutarate dehydrogenases.

Prescribing in practice

In suspected Wernicke's encephalopathy, give parenteral thiamine before or alongside any intravenous glucose, since glucose given first can precipitate or worsen the condition.
Anaphylaxis can rarely occur with intravenous administration, so give it with appropriate observation and resuscitation facilities available.
High-dose parenteral replacement is preferred for treatment of established deficiency, with oral therapy used for maintenance or milder deficiency.

Monitoring

Monitor clinical response, particularly neurological status in Wernicke's encephalopathy, rather than routine blood levels.

Counselling the patient

Replacement corrects a vitamin deficiency and is important if your diet has been poor or with heavy alcohol use.
Report any rash or breathlessness during an injection immediately.
Continue treatment for the full course advised, even once you feel better.

Evidence & guidelines

Thiamine is the established treatment for thiamine deficiency, and giving it before glucose in suspected Wernicke's encephalopathy is standard guidance.

Reference: NICE CG100/NG32; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Pathways