thiamine (vitamin B1)

introduction

thiamine is an essential vitamin involved in carbohydrate metabolism, acting as a coenzyme in reactions such as the decarboxylation of alpha-keto acids, particularly of pyruvate and alpha-keto-glutarate, and in the direct oxidating pathway of glucose metabolism
magnesium is an essential cofactor of thiamine
adult normal dietary requirements 1-2mg/day
it is not stored to any appreciable extent in the body and amounts in excess of the body's requirements are excreted in the urine as unchanged thiamine or as the metabolite, pyrimidine and thus toxicity is not an issue.

restricted diets
gastrointestinal diseases
hyperemesis gravidarum
extensive burns
diabetes
impaired kidney or liver function
hyperthyroidism
alcoholism - inadequate dietary intake, reduced GIT absorption, decreased hepatic storage, and impaired utilization
benign mammary dysplasia
TPN
diuretics such as frusemide / furosemide / Lasix

may be iatrogenically precipitated by glucose loading in patients with unsuspected thiamine deficiency
classic triad:
- encephalopathy
- oculomotor dysfunction - horizontal nystagmus, bilateral lateral rectus palsy, and conjugate gaze palsies
- ataxia with wide-based slow gait

a long term consequence of Wernicke's encephalopathy which generally results in severe disability and often the need for long term care
a neuropsychiatric disorder associated with:
- memory disturbances
  - significant deficits in anterograde and retrograde memory
  - immediate memory is maintained, but short-term memory is diminished with intact sensorium.
- confabulation
  - patients fabricating stories in the setting of clear consciousness.
  - usually provoked confabulation whereas spontaneous confabulation is generally more associated with Wernicke's encephalopathy

most common in Asia where the diet consists of a high intake of polished rice which is deficient in thiamine
two types:
- “dry form”:
  - mainly neurologic symptoms with peripheral neuropathy
  - more common form in Western cultures
- “wet form”
  - high output cardiac failure with peripheral oedema
    - due to vasodilatation resulting in reduced systemic vascular resistance
  - mainly occurs in Asia

oral dose is 50-100mg per day for adults
those with alcoholism or GIT conditions may not absorb oral doses and should be given iv doses of 100mg thiamine by infusion over 30 minutes, BEFORE glucose or dextrose administration to avoid precipitating Wernicke's encephalopathy.

iv thiamine 500mg infused over 30min, 3 times a day for 1st 2 days then once daily for 5 further days (these doses can be im), then 100mg/day orally
magnesium and other vitamin B supplements