Thiamine (Vitamin B1)

Thiamine is vitamin B1, a water-soluble nutrient essential to normal energy metabolism and neurologic function. Veterinary replacement is used for deficiency caused by inadequate intake, impaired utilization or thiamine antagonism. A major large-animal application is thiamine-responsive polioencephalomalacia. It is also supplied in B-complex preparations and selected toxicology-support protocols.

Group

Water-soluble vitamin

Mechanism of Action

Thiamine is converted to thiamine pyrophosphate, a cofactor for enzymes involved in carbohydrate oxidation and the pentose-phosphate pathway. These include pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase and transketolase. Replacement restores energy production and related metabolic pathways in deficient tissue, particularly the nervous system. In ethylene glycol metabolism, thiamine-dependent pathways provide a proposed route toward less harmful metabolites.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Vitamin B1 supplementation	10–100 mg/animal	PO	Every 24 h
Vitamin B1 supplementation	12.5–50 mg/animal	IM, SC	Every 24 h
Thiamine deficiency	5–50 mg/animal	IM, SC, IV		Injectable route depends on exact formulation; IV very slowly.
Thiamine deficiency	1–2 mg/animal	IM
Thiamine deficiency	2 mg/kg	PO	Every 24 h
Clinical thiamine deficiency	100–250 mg/animal	SC	Every 12 h	Several days until regression of signs; reassess diagnosis and recovery.
Ethylene glycol antidotal adjunct	100 mg/animal	PO	Every 24 h

Cats

Use / stage	Dose	Route	Schedule	Instructions
Vitamin B1 supplementation	5–30 mg/animal	PO	Every 24 h	Maximum 50 mg/day; The daily ceiling applies to the combined amount of all doses.
Vitamin B1 supplementation	12.5–25 mg/animal	IM, SC	Every 24 h
Clinical thiamine deficiency	100–250 mg/animal	SC	Every 12 h	Several days until regression of signs; reassess diagnosis and recovery.
Thiamine deficiency — Initial	10–20 mg/kg	IM, SC	Every 8–12 h	Until signs abate.
Thiamine deficiency — Maintenance	10 mg/kg	PO	Every 24 h	Up to 21 days

Sheep

Use / stage	Dose	Route	Schedule	Instructions
Vitamin B1 supplementation	12.5–25 mg/animal	IM	Every 24 h	Lambs.
Vitamin B1 supplementation	65–125 mg/animal	IM	Every 24 h	Adults.
Polioencephalomalacia — Initial	10 mg/kg	IV	Once	Very slowly IV.
Polioencephalomalacia — Maintenance	10 mg/kg	IM	Every 12 h	Up to 3 days; Reported 2-3 days; reassess if response absent.
Thiamine deficiency	10–20 mg/kg	IM, SC	Every 8 h
Thiamine deficiency fixed alternative	20–200 mg/animal	IM, SC, IV

Pigs

Use / stage	Dose	Route	Schedule	Instructions
Vitamin B1 supplementation	65–125 mg/animal	IM	Every 24 h
Thiamine deficiency	5–100 mg/animal	IM, SC, IV

Cattle

Use / stage	Dose	Route	Schedule	Instructions
Vitamin B1 supplementation	37.5–65 mg/animal	IM	Every 24 h	Calves.
Vitamin B1 supplementation	125–250 mg/animal	IM	Every 24 h	Adults.
Polioencephalomalacia — Initial	10 mg/kg	IV	Once	Very slowly IV.
Polioencephalomalacia — Maintenance	10 mg/kg	IM	Every 12 h	Up to 3 days; Reported 2-3 days; reassess if response absent.
Thiamine deficiency	10–20 mg/kg	IM, SC	Every 8 h
Lead poisoning adjunct	2 mg/kg	IM	Every 6 h	With calcium EDTA treatment; total daily thiamine amount 8 mg/kg.

Horses

Use / stage	Dose	Route	Schedule	Instructions
Vitamin B1 supplementation	37.5–65 mg/animal	IM	Every 24 h	Foals.
Vitamin B1 supplementation	125–250 mg/animal	IM	Every 24 h	Adults.
Thiamine deficiency	0.5–5 mg/kg	IV, IM, PO
Thiamine deficiency fixed alternative	100–1000 mg/animal	IM, SC, IV		Exact formulation determines injectable suitability.

Goats

Use / stage	Dose	Route	Schedule	Instructions
Polioencephalomalacia — Initial	10 mg/kg	IV	Once	Very slowly IV.
Polioencephalomalacia — Maintenance	10 mg/kg	IM	Every 12 h	Up to 3 days; Reported 2-3 days; reassess if response absent.
Thiamine deficiency	10–20 mg/kg	IM, SC	Every 8 h

Llamas

Use / stage	Dose	Route	Schedule	Instructions
Amprolium-associated deficiency prevention	10 mg/kg	SC	Every 24 h	Begin after day 5 of amprolium in reported E. macusaniensis course.

Alpacas

Use / stage	Dose	Route	Schedule	Instructions
Amprolium-associated deficiency prevention	10 mg/kg	SC	Every 24 h	Begin after day 5 of amprolium in reported E. macusaniensis course.

Indications

Treatment of confirmed or suspected thiamine deficiency in veterinary patients.
Treatment of thiamine-responsive polioencephalomalacia in ruminants.
Replacement in selected deficiency states associated with thiaminases, poor nutrition or thiamine-antagonist exposure.
Adjunctive metabolic support in selected ethylene glycol intoxications, with limited evidence of an independent outcome benefit.
Selected adjunctive support in lead poisoning where a thiamine-responsive component is suspected, with limited clinical evidence.

Contraindications

Rapid IV administration can provoke anaphylactic reactions.

Interactions

Acidic hydrochloride solutions may be incompatible with alkalinizing mixtures.

Adverse effects

Routine supplementation is usually well tolerated; serious reactions can follow rapid IV injection.

Toxicity

Rapid IV thiamine can cause anaphylactoid reactions. Very large exposure may cause hypotension, respiratory depression or neuromuscular effects; provide supportive assessment.

Preparations

Preparation	Form	Strength	Route
Thiamine hydrochloride injection 100 mg/mL	Injection	100 mg / mL	IM, SC
Thiamine hydrochloride injection 500 mg/mL	Injection	500 mg / mL	IM, SC
Thiamine elixir 250 mcg/5 mL	Oral Liquid	250 mcg / 5 mL	PO

Monitoring and Administration

Use the supplied oral, IM and SC regimens; IV administration, if used, must be very slow. Protect from light and assess compatibility before adding to fluids.

Foal perinatal-asphyxia protocol includes thiamine 1 g in 1 L IV fluid once daily. Feline hepatic-lipidosis fluids may contain 100 mg/L plus other B vitamins. Exact delivered fluid volume and full coingredient composition are needed for a combination preparation. A parenteral-nutrition vitamin list gives cyanocobalamin 5 mg/mL, which needs unit confirmation before normalization.