Thiamine Hydrochloride — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	10-100 mg/day	q12-24h	Duration: Until clinical signs resolve, then as needed Notes: For deficiency, higher doses may be used initially. For supportive therapy, lower doses are often used.
Dog	IV/IM/SC	10-50 mg/kg	q12-24h	Duration: For acute deficiency, until clinical improvement, then switch to oral Notes: IV administration should be slow. For severe neurological signs, use IV initially.
Cat	PO	10-50 mg/day	q12-24h	Duration: Until clinical signs resolve, then as needed Notes: Cats are more sensitive to deficiency; ensure adequate dosing.
Cat	IV/IM/SC	10-25 mg/kg	q12-24h	Duration: For acute deficiency, until clinical improvement, then switch to oral Notes: IV administration should be slow.
Horse	PO	1-3 g/day	q24h	Duration: As needed Notes: For deficiency or supportive therapy.
Horse	IV/IM	10-20 mg/kg	q12-24h	Duration: For acute deficiency, until clinical improvement Notes: IV administration should be slow.
Cattle	IV/IM/SC	10-20 mg/kg	q12-24h	Duration: For PEM, treat for 3-5 days, then reassess Notes: For PEM, give IV initially, then IM/SC. Also treat herdmates prophylactically.
Cattle	PO	1-3 g/day	q24h	Duration: For prevention, as needed Notes: Oral thiamine may be degraded in rumen; parenteral is preferred for treatment.
Sheep/Goats	IV/IM/SC	10-20 mg/kg	q12-24h	Duration: For PEM, treat for 3-5 days Notes: Similar to cattle.
Rabbit	PO/SC/IM	25-50 mg/kg	q12-24h	Duration: As needed Notes: Use with caution in rabbits; ensure proper hydration.
Birds	PO/IM	25-50 mg/kg	q12-24h	Duration: As needed Notes: For deficiency, use parenteral initially.

Clinical Indications & Species Uses

General Indications

Treatment of thiamine deficiency
Supportive therapy in conditions with increased metabolic demand
Adjunct in hepatic disease and cardiac disease

Dog (Canine)

Treatment and prevention of thiamine deficiency
Anorexia and weight loss
Neurological disorders due to thiamine deficiency (e.g., Chastek paralysis)
Supportive therapy in hepatic disease
Adjunct in congestive heart failure (to improve myocardial metabolism)

Cat (Feline)

Treatment and prevention of thiamine deficiency
Anorexia and weight loss
Neurological signs (e.g., vestibular signs, seizures) due to thiamine deficiency
Supportive therapy in hepatic disease
Adjunct in cardiac disease

Horse (Equine)

Treatment of thiamine deficiency (e.g., from bracken fern toxicity)
Supportive therapy in neurological conditions (e.g., EPM, equine motor neuron disease)
Anorexia and weight loss
Adjunct in hepatic disease

Cattle (Bovine)

Treatment of polioencephalomalacia (PEM) due to thiamine deficiency
Supportive therapy in neurological diseases
Anorexia and ruminal dysfunction
Prevention of PEM in high-risk herds

Small Ruminants (Sheep / Goat)

Treatment of polioencephalomalacia (PEM) in sheep and goats
Supportive therapy in neurological diseases
Anorexia and ruminal dysfunction

Rabbit & Small Mammals

Treatment and prevention of thiamine deficiency
Supportive therapy in gastrointestinal stasis (as part of a comprehensive treatment plan)

Avian & Poultry

Treatment and prevention of thiamine deficiency (e.g., in birds fed all-meat diets)
Supportive therapy in neurological signs (e.g., opisthotonos)

Exotic & Other Species

Treatment of thiamine deficiency in exotic animals (e.g., reptiles, small mammals) when indicated
Supportive therapy in neurological disorders

Pharmacology & Mechanism of Action

Drug Class: Vitamin | Pharmacological Group: Water-soluble vitamin (B1)

Mechanism of Action: Thiamine (vitamin B1) is a water-soluble vitamin that is converted in the body to the coenzyme thiamine pyrophosphate (TPP), also known as thiamine diphosphate (TDP). TPP is essential for several enzymatic reactions in carbohydrate metabolism, including the oxidative decarboxylation of pyruvate to acetyl-CoA (pyruvate dehydrogenase complex), the oxidative decarboxylation of alpha-ketoglutarate in the citric acid cycle (alpha-ketoglutarate dehydrogenase complex), and the transketolase reaction in the pentose phosphate pathway. By facilitating these reactions, thiamine is critical for energy production, particularly in tissues with high glucose utilization such as the brain, heart, and nervous system. Deficiency leads to impaired carbohydrate metabolism, accumulation of pyruvate and lactate, and subsequent cellular dysfunction, especially in the central nervous system.

Pharmacodynamics: Thiamine acts as a coenzyme in key metabolic pathways, promoting normal growth and development, maintaining proper function of the heart, nervous system, and muscles. It also plays a role in nerve impulse transmission and in the synthesis of acetylcholine. In veterinary medicine, thiamine supplementation corrects deficiencies and supports metabolic processes. Pharmacodynamic effects are primarily seen in correction of clinical signs associated with thiamine deficiency, such as neurological signs, cardiac dysfunction, and gastrointestinal disturbances.

⚡ Pharmacokinetics Summary

Absorption: Thiamine hydrochloride is readily absorbed from the gastrointestinal tract, primarily in the proximal small intestine. Absorption is dose-dependent and saturable; at high doses, passive diffusion may occur. In ruminants, thiamine is also synthesized by ruminal microorganisms, but dietary supplementation is often necessary in cases of deficiency.

Distribution: Thiamine is widely distributed throughout the body, with highest concentrations in the liver, heart, brain, and kidneys. It crosses the blood-brain barrier and is also distributed into milk. In the body, it is primarily stored as TPP in tissues, but total body stores are limited, and deficiency can develop within weeks.

Metabolism: Thiamine is phosphorylated to TPP in the liver and other tissues by the enzyme thiamine pyrophosphokinase. It is not significantly metabolized otherwise; the active form is TPP.

Excretion: Thiamine and its metabolites are excreted primarily in the urine. In humans, the half-life is about 9-18 days, but in animals it is shorter. In dogs, the half-life is approximately 2-3 hours for the parent compound, but the active coenzyme has a longer duration. Excretion is increased with high doses.

Half-Life: Dogs: ~2-3 hours (parent compound); Cats: ~2-4 hours; Horses: ~1-2 hours; Ruminants: variable, but rapid.

Bioavailability: Oral bioavailability is variable and dose-dependent; it is enhanced by food. In monogastric animals, oral absorption is efficient at low doses, but decreases with high doses. In ruminants, oral thiamine may be degraded by ruminal microorganisms, so parenteral administration is often preferred for therapeutic use.

Protein Binding: Thiamine is minimally bound to plasma proteins (<10%).

Available Formulations & Strengths

Oral Tablet 50 mg, 100 mg, 250 mg (PO)

Oral Capsule 100 mg, 250 mg (PO)

Injectable Solution 100 mg/mL, 200 mg/mL, 250 mg/mL (IV/IM/SC)

Oral Powder Various (e.g., 500 mg/g) (PO)

Contraindications & Clinical Warnings

Contraindications:

Known hypersensitivity to thiamine or any component of the formulation
In animals with a history of allergic reactions to thiamine (rare)

Warnings & Clinical Precautions:

Use with caution in animals with renal impairment, as thiamine metabolites may accumulate.
Parenteral administration may cause pain at injection site; administer slowly.
In ruminants, oral thiamine may be degraded by ruminal microorganisms; parenteral administration is preferred for therapeutic use.
Thiamine requirements are increased in animals with fever, hyperthyroidism, liver disease, or during pregnancy/lactation.
Do not mix thiamine with alkaline solutions or sulfites, as it may be inactivated.
Use in animals with thiamine deficiency may cause rapid improvement; monitor for refeeding syndrome in severely debilitated animals.

Adverse Effects & Reactions

Common:

Pain at injection site
Local irritation after IM/SC injection
Gastrointestinal upset (rare with oral administration)

Serious / Severe:

Anaphylactic reactions (rare but possible, especially after IV administration)
Cardiovascular collapse (with rapid IV administration)

Rare:

Allergic dermatitis
Angioedema
Respiratory distress

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Furosemide	May increase urinary excretion of thiamine, potentially worsening deficiency.	Moderate
Antacids (e.g., sodium bicarbonate)	May inactivate thiamine in the gastrointestinal tract, reducing absorption.	Mild
Sulfites (as preservatives)	May degrade thiamine; avoid mixing in solutions containing sulfites.	Moderate
Neuromuscular blocking agents	Thiamine may enhance the effects of neuromuscular blockers (theoretical).	Mild

Overdose & Toxicity Management

Signs of Toxicity:

Thiamine is water-soluble and excess is excreted in urine; toxicity is rare.
Signs of overdose may include: nausea, vomiting, diarrhea, and in severe cases, neurological signs (e.g., tremors, seizures) due to rapid metabolic shifts.
Rapid IV administration may cause hypotension, cardiac arrhythmias, or anaphylactoid reactions.

Emergency Treatment Protocol: Treatment is symptomatic and supportive. Discontinue thiamine administration and provide supportive care. Monitor vital signs and treat anaphylaxis with epinephrine and corticosteroids if needed. In cases of severe overdose, intravenous fluids may be administered to enhance excretion. There is no specific antidote.

Food Animal Withdrawal Times

🥩 Meat: 0 days🥛 Milk: 0 days🥚 Eggs: 0 days

Thiamine is a vitamin and is generally considered to have zero withdrawal times in food animals. However, always follow label instructions and local regulations. For extra-label use, consult a veterinarian.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature (20-25°C or 68-77°F), protect from light and moisture.

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light and moisture. Keep container tightly closed. Do not freeze injectable solutions. Discard any unused portion after opening.

Dispensing Status: Over-The-Counter (OTC)

Approval Status: Thiamine hydrochloride is FDA-approved for use in veterinary medicine as a prescription or OTC product, depending on formulation. Many products are approved for use in dogs, cats, horses, and food animals.

Extra-Label (Off-Label) Use: Thiamine is a vitamin and is generally available over-the-counter. However, extra-label use in food animals must comply with AMDUCA regulations. Withdrawal times may need to be extended if used at higher doses or for prolonged periods. Consult a veterinarian for guidance.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Thiamine hydrochloride is a water-soluble vitamin essential for carbohydrate metabolism. Deficiency can occur due to inadequate dietary intake, increased metabolic demand, or ingestion of thiaminases (e.g., in raw fish, bracken fern). Clinical signs of deficiency vary by species but often include neurological signs (e.g., opisthotonos, ataxia, seizures), anorexia, and cardiac abnormalities. In ruminants, polioencephalomalacia (PEM) is a common manifestation. Treatment involves prompt administration of thiamine, preferably parenterally, along with supportive care. In food animals, thiamine is often used to treat PEM and is administered at high doses. Thiamine is generally safe with a wide margin of safety, but rapid IV administration should be avoided. It is important to address the underlying cause of deficiency and ensure adequate dietary intake. Thiamine is also used as a supportive therapy in various conditions, including hepatic disease and cardiac disease, due to its role in energy metabolism. Always follow label instructions and consult a veterinarian for appropriate dosing and treatment protocols.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)