Thiamin, Vitamin B1 : Interactions

by MedlinePlus

(Page 4 of 4)

Interactions with Drugs:

Phenytoin (Dilantin): Reduced levels of thiamin in blood and cerebrospinal fluid have been reported in individuals taking phenytoin for extended periods of time. However, thiamin supplementation beyond the Recommended Daily Allowance is not currently universally recommended in patients taking phenytoin.

Antacids: May lower thiamin levels in the body by decreasing absorption and increasing excretion or metabolism.

Barbiturates: Barbiturates may lower thiamin levels in the body by decreasing absorption and increasing excretion or metabolism.

Diuretics: Loop diuretics, particularly furosemide (Lasix), have been associated with decreased thiamin levels in the body by increasing urinary excretion (and possibly by decreasing absorption and increasing metabolism). Examples of other loop diuretics include bumetanide (Bumex), ethacrynic acid (Edecrine), and torsemide (Demadex). Theoretically, this effect may also occur with other types of diuretics, including thiazide diuretics such as chlorothiazide (Diuril), chlorthalidone (Hygroton, Thalitone), hydrochlorothiazide (HCTZ, Esidrix, HydroDIURIL, Ortec, Microzide), indapamide (Lozol), and metolazone (Zaroxolyn); or potassium-sparing diuretics such as amiloride (Midamor), spironolactone (Aldactone), and triamterene (Dyrenium). Effects may be most pronounced with larger doses (for example Lasix 80mg) taken over extended periods of time. Assessment of thiamin status may be merited in such patients, although prophylactic thiamin supplementation beyond the Recommended Daily Allowance is not universally recommended at this time.

Tobacco: Tobacco use decreases thiamin absorption and may lead to decreased levels in the body.

Neuromuscular blocking agents (NMBAs): Effects of NMBAs may be enhanced with concomitant (simultaneous) use of thiamin.

Antibiotics: Some antibiotics destroy gastrointestinal flora (normal bacteria in the gut) which manufacture some B vitamins. In theory, this may decrease the amount of thiamin available to humans, although the majority of thiamin is obtained through the diet (not via bacterial production). This interaction is likely not clinically relevant, and patients receiving antibiotics are generally not advised to take additional thiamin supplementation.

Birth control pills (oral contraceptives/OCPs): Oral contraceptives may decrease levels of some B vitamins, vitamin C, and zinc in the body. Some studies suggest slight decreases in thiamin levels with oral contraceptive use, while other research has found no significant effects. Additional thiamin supplementation beyond the Recommended Daily Allowance is generally not considered necessary in women taking oral contraceptives.

Fluorouracil (5-fluorouracil, 5-FU, Adrucil): The cancer chemotherapy drug 5-fluorouracil (5-FU) inhibits the phosphorylation of thiamin to thiamin pyrophosphate (TPP), interfering with activation of thiamine and possibly increasing its breakdown. People receiving fluorouracil-containing chemotherapy regimens may be at risk for developing symptoms and signs of thiamine deficiency. In addition, chemotherapy patients may be at an elevated risk of developing vitamin deficiencies due to decreased dietary intake. There is not enough evidence to routinely recommend thiamin supplementation in patients receiving 5-FU, although a multivitamin including thiamin is generally regarded as being reasonable.

Metformin (Glucophage): In theory, metformin may reduce thiamine activity, and based on animal research, taking thiamin and metformin together may contribute to the risk of lactic acidosis. Although there is no conclusive evidence in humans, caution is warranted.

Interactions with Herbs and Dietary Supplements:

Betel nut(Areca catechu L.):Consumption of betel nuts may reduce thiamine activity due to chemical inactivation, and may lead to symptoms and signs of thiamin deficiency.

Horsetail( Equisetum arvense L.): Horsetail contains a thiaminase-like compound that can destroy thiamine in the stomach, and theoretically causes symptomatic thiamine deficiency. Horsetail products are available without this property, and for example, the Canadian government requires that horsetail products be certified free of thiaminase activity.

Diuretic herbs: In theory, diuretic herbs may decrease thiamin levels in the body by increasing urinary excretion. Examples of herbs with possible diuretic activity include artichoke, celery, corn silk, couchgrass, dandelion, elder flower, horsetail, juniper berry, kava, shepherd's purse, uva ursi, and yarrow.

Interactions with Foods:

Alcohol: Alcohol use decreases thiamin absorption and may lead to decreased levels in the body.

Carbonated beveragesand foods or beverages with citrates may decrease the effects of thiamin in the body.

Coffee, tea: Chronic intake of polyphenols such as tannins in coffee and tea may convert thiamin to an unabsorbable and inactive form, and theoretically can worsen or cause thiamin deficiency. However, this interaction does not appear to be clinically relevant in industrialized countries where most individuals consume adequate dietary thiamin and ascorbic acid (which prevents this interaction). This interaction has been described in Asian populations which chew fermented tea leaves.

Raw seafood: Raw freshwater fish and shellfish contain thiaminase enzymes that destroy thiamine. Frequent ingestion of raw fish or shellfish can contribute to thiamine deficiency. Cooking destroys these enzymes, and therefore consumption of cooked seafood does not appear to affect thiamine levels.

Interactions with Laboratory Tests:

Theophylline serum levels:Large amounts of thiamine can interfere with Schack and Waxler spectrophotometric determination of serum theophylline concentrations.

Uric acid: Thiamine can cause false positive results in the phosphotungstate method for uric acid determination.

Urobilinogen: Thiamine can cause false positive results in the urine spot test with Ehrlich's reagent for urobilinogen.

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