Skip to content
ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Vitamin B1 Supplement Pregnancy: UK SPC §4.6, verbatim (this is the whole section): 'No adverse effects have been reported at recommended doses when used as clinically indicated. Animal studies are insufficient with respect to reproductive toxicity (see section 5.3). The potential risk for humans is unknown. Caution should be exercised when prescribing to pregnant women.' The SPC gives no breast-feeding statement in the fetched section. The US injection label separately in this bundle addresses a pregnancy indication (neuritis of pregnancy) but it was not used here.

Thiamine (Vitamin B1)

Brand names: Pabrinex (IV/IM — high-potency), Thiamine Tablets 100mg (oral)

Thiamine (vitamin B1) is a water-soluble vitamin given to prevent and treat thiamine deficiency states, most importantly Wernicke's encephalopathy and Korsakoff's syndrome, commonly in the context of alcohol dependence 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: SCOPE — this dose covers ONLY the intravenous high-potency Pabrinex preparation, which is this page's primary (emergency) route. The oral thiamine tablets and the intramuscular high-potency preparation that this page also lists are NOT dosed by the source used here and carry no figure on this record. ADULTS AND ELDERLY — rapid therapy of severe depletion or malabsorption of the water-soluble vitamins B and C, particularly in alcoholism, where a severe depletion of thiamine can lead to Wernicke's encephalopathy: 2 to 3 pairs of 5 ml ampoules (1 pair = ampoule number 1 + ampoule number 2), i.e. 10 ml from Ampoule Number 1 PLUS 10 ml from Ampoule Number 2, OR 15 ml from Ampoule Number 1 PLUS 15 ml from Ampoule Number 2, diluted with 50 ml to 100 ml of infusion solution (physiological saline or glucose 5%) and administered over 30 minutes every 8 hours, or at the discretion of the physician.
Route: Intravenous infusion only. §4.4, verbatim: 'This medicine is for injection into a vein only and should not be given by any other route.' Dilute before use and administer by drip infusion — equal volumes of the contents of ampoules number 1 and 2 added to 50 ml to 100 ml physiological saline or 5% glucose and infused over 30 minutes. Infusing over 30 minutes is itself a safety measure to minimise allergic reactions. Care should be taken to ensure that the route of administration used (intramuscular or intravenous) is that intended — reports of unintentional administration by the wrong route have been received.
Frequency: Every 8 hours for the severe-depletion / Wernicke's indication, or at the discretion of the physician
Max: 3 pairs of 5 ml ampoules (15 ml from Ampoule Number 1 plus 15 ml from Ampoule Number 2) every 8 hours — the top of the range §4.2 states for this indication. The SPC gives no other ceiling and states no thiamine milligram maximum.
NO MILLIGRAM FIGURE IS PUBLISHED, DELIBERATELY. The fetched §4.2 expresses every dose in ampoule pairs and millilitres and never states the thiamine content in milligrams, so no mg number can be quoted from this bundle. The milligram-per-dose thiamine figure previously carried on this page (an IV mg value) does not appear anywhere in the fetched sections and has NOT been reinstated — the numeral is deliberately not repeated here so that no downstream parser can lift it. Dose in ampoule pairs, as the label does. RECOVERED SOURCE — the previous hold reason on this draft is now STALE. That hold was recorded because the bundle then held only an oral 'Thiamine Hydrochloride 100 mg Tablets' SPC (which never mentions Wernicke's encephalopathy) plus a US injection label whose Wernicke-Korsakoff figures are an order of magnitude below UK practice. The bundle now holds the UK SPC for 'Pabrinex/Vitamin B&C Intravenous High Potency, Concentrate for Solution for Infusion' — the exact brand this page names first, licensed for exactly this page's headline indication and route. WHAT THIS SOURCE STILL DOES NOT COVER: it is the INTRAVENOUS high-potency preparation, and §4.4 restricts it to the intravenous route, so it does not source the IM route this page lists (a separate intramuscular high-potency product would be needed) and it says nothing about oral thiamine tablets. Those two routes remain unsourced. THIS IS A COMBINED PREPARATION, not thiamine alone — it is a high-potency vitamin B and C product, and §4.5 notes 'The content of pyridoxine may interfere with the effects of concurrent levodopa therapy.' OTHER INDICATIONS IN THE SAME §4.2, recorded but NOT this page's primary dose: psychosis following narcosis or E.C.T. and toxicity from acute infections — 1 pair of 5 ml ampoules (5 ml Ampoule Number 1 plus 5 ml Ampoule Number 2) diluted with 50 ml to 100 ml infusion solution and administered over 30 minutes twice daily for up to 7 days; haemodialysis — 1 pair of 5 ml ampoules diluted the same way and administered over 30 minutes once every two weeks at the end of dialysis. PRESENTATION CHECK: in common with all parenteral products each ampoule should be visually inspected prior to administration and should not be used if particulates are present. The US injection label and the WHO eEML reference also present in this bundle were NOT used for any figure above.

Paediatric dose

Route: Intravenous infusion, as for adults — dilute equal volumes of ampoules number 1 and 2 in 50 ml to 100 ml physiological saline or 5% glucose and infuse over 30 minutes
Frequency: As for the corresponding adult indication
Max: No separate paediatric ceiling is stated — the paediatric maximum is the stated fraction of the adult maximum for the child's age band
THE LABEL GIVES NO PER-KILOGRAM PAEDIATRIC FIGURE — dosePerKg is therefore null and must stay null; the paediatric dose here is a FRACTION OF THE ADULT DOSE by age band, so a weight calculator cannot be used for it. §4.2 Paediatric population, verbatim: 'Vitamin B&C Intravenous High Potency, Concentrate for Solution for Infusion is rarely indicated for administration to children; however, suitable doses are as follows: Under 6 years quarter of the adult dose; 6 - 10 years third of the adult dose; 10 - 14 years half to two thirds of the adult dose; 14 years and over as for the adult dose.' Note the label's own opening caveat that the product is rarely indicated in children. Verify any under-18 use against a children's formulary and current prescribing references.

Dose adjustments

Renal

Not stated. No renal-impairment dosing statement appears in any fetched section of this SPC. §4.2 does give a haemodialysis regimen — 1 pair of 5 ml ampoules diluted with 50 ml to 100 ml infusion solution and administered over 30 minutes once every two weeks at the end of dialysis — but that is a separate listed indication, not a dose adjustment for renal impairment.

Hepatic

Not stated — no hepatic-impairment statement appears in any fetched section of this SPC.

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 the active substances or to any of the excipients listed in section 6.1 — this is the whole of §4.3
  • Route restriction, §4.4: 'This medicine is for injection into a vein only and should not be given by any other route'
  • Do not use if particulates are present on visual inspection of the ampoule (§4.4)
  • IMPORTANT §4.4 QUALIFIER, verbatim: 'Although potentially serious allergic adverse reactions such as anaphylactic shock may occur rarely during, or shortly after, parenteral administration... such rare occurrence of serious allergic reactions should not preclude the use of Vitamin B&C IVHP in patients who need treatment by this route of administration particularly those at risk of Wernicke's encephalopathy - for whom treatment with parenteral thiamine is essential'
  • Caution in pregnancy — §4.6: 'Caution should be exercised when prescribing to pregnant women'

Side effects

  • Unknown frequency — hypersensitivity, including anaphylaxis, rash and urticaria
  • Unknown frequency — paraesthesia
  • Unknown frequency — hypotension
  • Unknown frequency — injection site reactions, including pain and swelling
  • §4.4: potentially serious allergic adverse reactions such as anaphylactic shock may occur rarely during, or shortly after, parenteral administration. Initial warning signs of a reaction are sneezing or mild asthma, and the administration of further injections to such patients may give rise to anaphylactic shock

Monitoring

  • Facilities for treating anaphylactic reactions should be available whenever this product is administered (§4.4)
  • Watch for the initial warning signs of a reaction — sneezing or mild asthma — and note that further injections in a patient who has shown these may give rise to anaphylactic shock (§4.4)
  • Administer by infusion over a period of 30 minutes; §4.4 states this specifically 'to minimise the risk of such events'
  • Confirm the intended route before administration — reports of unintentional administration by the wrong route have been received, although these incidents have not been associated with serious adverse reactions (§4.4)
  • Visually inspect each ampoule prior to administration and do not use if particulates are present (§4.4)
  • Interaction to review: the pyridoxine content may interfere with the effects of concurrent levodopa therapy (§4.5)

Clinical monograph

How it works

As its active form thiamine pyrophosphate, it is an essential cofactor for enzymes of carbohydrate metabolism, and replacement restores normal cerebral and peripheral energy metabolism.

Prescribing in practice

  • In suspected or established Wernicke's encephalopathy, give parenteral thiamine before or with any glucose, since administering carbohydrate first can precipitate or worsen the condition.
  • Parenteral high-potency thiamine carries a small risk of anaphylaxis, so administer where facilities to manage this are available.
  • Maintain a low threshold for treatment in alcohol-dependent and malnourished patients, as deficiency is frequently underdiagnosed.

Monitoring

Monitor the clinical response of neurological and other deficiency features, and observe for hypersensitivity reactions during parenteral administration.

Counselling the patient

  • This vitamin replaces a deficiency that can affect the brain and nerves.
  • Attending for treatment is important even if you feel relatively well.
  • Report any rash or breathing difficulty during an injection.

Evidence & guidelines

Prompt thiamine replacement to prevent and treat Wernicke's encephalopathy is endorsed by NICE alcohol-use disorder guidance.

Reference: Royal College of Physicians Alcohol Guidelines; NICE CG100 (Alcohol Use Disorders); SIGN 74; 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).

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways