thiamine hydrochloride (vitamin B1)

Pharmacologic classification: water-soluble vitamin
Therapeutic classification: nutritional supplement
Pregnancy risk category A (C if more than RDA)

Available forms
Available by prescription only
Injection: 1-ml ampules (100 mg/ml), 1-ml vials (100 mg/ml), 1-ml syringes (100 mg/ml), 2-ml vials (100 mg/ml), 10-ml vials (100 mg/ml), 30-ml vials (100 mg/ml)

Available without a prescription
Tablets: 25 mg, 50 mg, 100 mg, 250 mg, 500 mg
Tablets (enteric-coated): 20 mg

Indications and dosages
  The RDA of thiamine is as follows:
Neonates and infants up to age 6 months: 0.3 mg daily.
Infants ages 6 months to 1 year: 0.4 mg daily.
Children ages 1 to 3: 0.7 mg daily.
Children ages 4 to 6: 0.9 mg daily.
Children ages 7 to 10: 1 mg daily.
Boys ages 11 to 14: 1.3 mg daily.
Boys and men ages 15 to 50: 1.5 mg daily.
Men age 51 and older: 1.2 mg daily.
Girls and women ages 11 to 50: 1.1 mg daily.
Women age 51 and older: 1 mg daily.
Pregnant women: 1.5 mg daily.
Breast-feeding women: 1.6 mg daily.
 Beriberi. Adults: 10 to 20 mg I.M., depending on severity (can receive up to 100 mg I.M. or I.V. for severe cases), t.i.d. for 2 weeks, followed by dietary correction and multivitamin supplement containing 5 to 30 mg thiamine daily in single dose or three divided doses for 1 month.
Children: 10 to 25 mg, depending on severity, I.M. daily for several weeks with adequate dietary intake.
 Anemia secondary to thiamine deficiency; polyneuritis secondary to alcoholism, pregnancy, or pellagra. Adults and children: P.O. dosage is based on RDA for age-group.
 Wernicke’s encephalopathy. Adults: Initially, 100 mg I.V., followed by 50 to 100 mg I.M. or I.V. daily.
 "Wet beriberi" with heart failure. Adults and children: 10 to 30 mg I.V. for emergency treatment.

Metabolic action: Exogenous thiamine is required for carbohydrate metabolism. Thiamine combines with ATP to form thiamine pyrophosphate, a coenzyme in carbohydrate metabolism and transketolation reactions. This coenzyme is also needed in the hexose monophosphate shunt during pentose utilization. One sign of thiamine deficiency is an increase in pyruvic acid. The body’s need for thiamine is greater when the carbohydrate content of the diet is high. Within 3 weeks of total absence of dietary thiamine, significant vitamin depletion can occur. Thiamine deficiency can cause beriberi.

Absorption: Absorbed readily after oral administration of small doses; after oral administration of a large dose, the total amount absorbed is limited to 4 to 8 mg. In patients with alcoholism, cirrhosis, or malabsorption, GI absorption of thiamine is decreased. When given with meals, GI drug absorption decreases, but total absorption remains the same. After I.M. administration, drug is absorbed rapidly and completely.
Distribution: Distributed widely into body tissues. When intake exceeds the minimal requirements, tissue stores become saturated. About 100 to 200 mcg of thiamine is distributed daily into the milk of breast-feeding women on a normal diet.
Metabolism: Metabolized in the liver.
Excretion: Excess thiamine is excreted in urine. After administration of large doses (more than 10 mg), both unchanged thiamine and metabolites are excreted in urine after tissue stores become saturated.

Route Onset Peak Duration
P.O., I.V., I.M. Unknown Unknown Unknown

Contraindications and precautions
Contraindicated in patients hypersensitive to thiamine products.

Drug-drug. Alkaline solutions, such as carbonates, citrates, and bicarbonates: Thiamine is incompatible with these solutions. Avoid use together.
Neuromuscular blockers: May enhance effects of these drugs. Monitor patient.
Neutral or alkaline solutions: Thiamine is unstable in these solutions. Don’t mix the drug in these solutions.
Sulfites: Solutions containing sulfites are incompatible with thiamine. Avoid use together.

Adverse reactions
CNS: restlessness.
CV: CV collapse, cyanosis.
EENT: tightness of throat (allergic reaction).
GI: nausea, hemorrhage.
Respiratory: pulmonary edema.
Skin: feeling of warmth, pruritus, urticaria, diaphoresis.
Other: angioedema, weakness, tenderness and induration following I.M. administration.

Effects on lab test results
None reported.

Overdose and treatment
Very large doses of thiamine administered parenterally may produce neuromuscular and ganglionic blockade and neurologic symptoms.
 Treatment is supportive.

Special considerations
• Total absence of dietary thiamine can produce a deficiency state in about 3 weeks.
• Accurate dietary history is important during vitamin replacement therapy.
• Before I.V. thiamine administration, an intradermal skin test should be performed if sensitivity is suspected.
 ALERT When giving large parenteral doses, keep epinephrine available.
• I.M. injection may be painful. Rotate injection sites.
• Monitor patient for adverse reactions, including injection site reactions.
• Monitor patient for symptom relief.
• Drug therapy may produce false-positive results in the phosphotungstate method for determination of uric acid and in urine spot tests with Ehrlich’s reagent for urobilinogen.
• Large doses of thiamine interfere with the Schack and Waxler spectrophotometric determination of serum theophylline levels.
• Store thiamine in light-resistant, nonmetallic container.
Breast-feeding patients
• Thiamine, in amounts that don’t exceed the RDA, is safe to use in breast-feeding women. It appears in breast milk and fulfills a nutritional requirement of the infant.

Patient education
• Inform patient of potential adverse reactions.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use