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Mechanism of Action
1.4 mg PO per day.
1.2 mg PO per day.
1.1 mg PO per day.
1 mg PO per day.
0.9 mg PO per day.
0.6 mg PO per day.
0.5 mg PO per day.
0.3 mg PO per day is the Adequate Intake (AI). An RDA has not been established.
0.2 mg/day PO is the Adequate Intake (AI). An RDA has not been established.
3 mg IV per day admixed with TPN.
NOTE: If beriberi occurs in a breast-fed infant, both the lactating mother and the infant should receive treatment for thiamine deficiency.
5—30 mg PO once daily or given in 3 divided doses for 1 month.
10—50 mg PO once daily for 2 weeks, then 5—10 mg PO once daily for 1 month.
5—30 mg IV or IM once daily or in 3 divided doses initially; then convert to 5—30 mg PO once daily or in 3 divided doses once patient is taking PO. Total treatment duration is 1 month.
10—25 mg IV or IM per day for 2 weeks, then 5—10 mg PO once daily for 1 month.
200 to 500 mg IV for at least 3 days or until there is no further improvement in symptoms.     The FDA-approved dosage is 100 mg IV, followed by 50 to 100 mg IM once daily until normal dietary intake is established.
100 mg PO once daily for 3 to 5 days.
100 mg IV or IM once daily for 3 to 5 days.
10 to 20 mg/day PO as a single dose. Up to 4 g/day in divided doses has been used.
It appears that no dosage adjustments are needed.
Patients on dialysis may have increased needs for thiamine.
Description: Thiamine, or vitamin B1, is a water-soluble vitamin found in such foods as yeast, cereal grains, legumes, peas, nuts, pork, and beef. Thiamine deficiency causes beriberi. Thiamine is also used to prevent peripheral neuritis associated with pellagra and pregnancy. This vitamin is also beneficial in treating metabolic disorders associated with subacute necrotizing encephalomyelopathy, branched-chain aminoacidopathy, and lactic acidosis associated with pyruvate carboxylase deficiency. Thiamine is considered a standard agent in the treatment of a patient with undiagnosed coma. Thiamine was approved by the FDA at its inception in 1938.
For storage information, see the specific product information within the How Supplied section.
Direct IV injection:
Continuous IV infusion:
Thiamine is relatively free from adverse reactions. The incidence of severe reactions to parenteral thiamine is estimated to be < 0.1%, even with undiluted IV push administration. In rare cases, thiamine hypersensitivity, including urticaria, anaphylactoid reactions, collapse, and death have occurred, primarily following repeated parenteral administration. Symptoms of sneezing or generalized pruritus may preceed more severe reactions. Pruritus appears to occur in approximately 1% of individuals receiving parenteral thiamine. There have also been reports of a feeling of warmth, urticaria, weakness, diaphoresis, nausea, restlessness, tightness of the throat, angioedema, cyanosis, pulmonary edema, and GI bleeding with parenteral administration.
The most common adverse reaction to parenteral thiamine administration is an injection site reaction. Pain, induration, and tenderness after IM injection can occur. Patients receiving IV thiamine may experience transient burning or pain immediately after injection into the IV site or IV line. Reactions related to IV thiamine administration can be minimized by slow IV administration into larger, more proximal veins with high flow rates. Injection site reactions are usually mild and transient, with no permanent consequence.
Wernicke's encephalopathy may be precipitated or worsened if intravenous glucose is administered to a thiamine-deficient patient. Thiamine (vitamin B1) should be administered prior to glucose. Clinicians should note that parenteral glucose should never be administered to a comatose patient without the prior administration of thiamine.
Thiamine is classified as FDA pregnancy risk category A. Appropriate maternal thiamine (vitamin B1) intake is encouraged during pregnancy, and no maternal or fetal complications associated with maternal dietary intake or supplementation to achieve adequate intake goals have been reported. As with other water-soluble vitamins, the pregnancy risk factor increases to FDA risk category C if the vitamin is used in dosages exceeding the Recommended Dietary Allowance (RDA) during pregnancy.
According to the manufacturer, caution should be exercised when thiamine is administered during breast-feeding. However, while thiamine is excreted in human milk, appropriate maternal intake of thiamine (vitamin B1) is important during lactation, and no maternal or fetal complications have been identified with maternal supplementation to achieve adequate intake goals during breast-feeding. Seizures have occurred in nursing infants of mothers with thiamine deficiency, although causality has not been established. Supplementation with thiamine is recommended in lactating women whose diets do not provide adequate amounts of thiamine. The American Academy of Pediatrics classifies thiamine as compatible with breast-feeding. Consider the benefits of breast-feeding, the risk of potential infant drug exposure, and the risk of an untreated or inadequately treated condition. If a breast-feeding infant experiences an adverse effect related to a maternally administered drug, healthcare providers are encouraged to report the adverse effect to the FDA.
Mechanism of Action: Thiamine combines with adenosine triphosphate (ATP) in the liver, kidneys, and leukocytes to produce thiamine diphosphate. Thiamine diphosphate acts as a coenzyme in carbohydrate metabolism, in transketolation reactions, and in the utilization of hexose in the hexose-monophosphate shunt. Without adequate thiamine, pyruvic acid does not undergo conversion to acetyl-CoA and cannot enter the Krebs cycle. Pyruvic acid accumulates in the blood and is subsequently converted to lactic acid, with the potential development of lactic acidosis. Diminished production of NADH in the Krebs cycle also results in lactic acid production through facilitation of anaerobic glycolysis.
Thiamine deficiency appears as a nonspecific syndrome: headache, nausea, malaise, myalgias. Severe thiamine deficiency causes beriberi. Beriberi can affect the cardiovascular system (wet beriberi) and the nervous system (dry beriberi and the Wernicke-Korsakoff syndrome). Cardiovascular manifestations include peripheral vasodilation, biventricular failure, and edema. Neurologic symptoms include neuropathy, ataxia, retrograde amnesia, impaired ability to learn, and confabulation. Once Korsakoff's syndrome appears, thiamine supplementation is successful in only half of the patients.
Thiamine is administered orally and by intramuscular or intravenous injection. Thiamine is widely distributed. Body storage of thiamine is limited to about 30 mg. Thiamine is distributed into breast milk at a rate of about 100—200 mcg daily from normal dietary intake. There is little excretion of thiamine or its metabolites at physiologic doses. Following large doses, saturation occurs, with subsequent renal excretion as pyrimidine.
Small oral doses are readily absorbed from the GI tract, but absorption of large doses is limited. Administration with food reduces the rate of absorption.
Following IM administration of thiamine, vitamin B1, absorption is rapid and complete.
Patients with cirrhosis have a decreased extent of absorption of thiamine, vitamin B1.
Alcoholics have a decreased extent of absorption of thiamine, vitamin B1.
Patients with malabsorption have a decreased extent of absorption of thiamine, vitamin B1.
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