Thiamine (Vitamin B1)
Thiamine hydrochloride
Also known as: Thiamilate · Horse Care Durvit B-1 Crumbles · Thia-Dex · Vitamin B-1 Powder · Vitamin B1 · Aneurine hydrochloride · Thiamin hydrochloride · Thiamine chloride · Thiamini hydrochloridum · Thiaminii chloridum · Thiamine hydrochloride
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Thiamine deficiency | 5-50 mg | IM, SC, or IV | Not specified | — | 🌎 NA |
| Thiamine deficiency | 1-2 mg | IM | Not specified | — | 🌎 NA |
| Thiamine deficiency | 2 mg/kg | PO | once daily | — | 🌎 NA |
| Thiamine deficiency | 100-250 mg | SC | twice daily | for several days until regression of symptoms with complete recovery | 🌎 NA |
| Adjunctive treatment for ethylene glycol toxicity | 100 mg/day | PO | daily | — | 🌎 NA |
- Thiamine deficiency: Depending on formulation
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Thiamine deficiency | 100-250 mg | parenterally | twice a day | — | 🌎 NA |
| Thiamine deficiency | 10-20 mg/kg | IM | Not specified | for several days | 🌎 NA |
| Adjunctive treatment of hepatic lipidosis | 100 mg of thiamine in one liter of crystalloid fluids | IV | Not specified | — | 🌎 NA |
| Thiamine deficiency | 100-250 mg | SC | twice daily | for several days until regression of symptoms with complete recovery | 🌎 NA |
| Thiamine deficiency | 10-20 mg/kg IM or SC two to three times daily until signs abate, then 10 mg/kg PO once daily | IM, SC, PO | two to three times daily, then once daily | 21 days for PO phase | 🌎 NA |
- Thiamine deficiency: Experimentally, as little as 1 mg is effective
- Adjunctive treatment of hepatic lipidosis: With additional soluble B vitamins. Indicated if neck ventroflexion is present.
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Prophylaxis when animals with E. macusaniensis treated with amprolium for >5 days (Camelids) | 10 mg/kg | SC | q24h | after the 5th day of amprolium | 🌎 NA |
- Prophylaxis when animals with E. macusaniensis treated with amprolium for >5 days (Camelids): For Camelids (NWC)
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Thiamine deficiency | 0.5-5 mg/kg | IV, IM or PO | Not specified | — | 🌎 NA |
| Thiamine deficiency | 100-1000 mg | IM, SC, or IV | Not specified | — | 🌎 NA |
| Adjunctive treatment of perinatal asphyxia syndrome (hypoxic ischemic encephalopathy) | 1 gram in one liter of fluids | IV | once a day | — | 🌎 NA |
| As part of a parenteral nutrition (PN) formula | 1-2 mL/45 kg daily | IV | daily | — | 🌎 NA |
- Thiamine deficiency: Depending on formulation
- Adjunctive treatment of perinatal asphyxia syndrome (hypoxic ischemic encephalopathy): For Foals
- As part of a parenteral nutrition (PN) formula: Using a specific B complex vitamin mix (thiamine 12.5 mg/mL) diluted in fluids or PN.
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Polioencephalomalacia | Initially, 10 mg/kg IV; then, 10 mg/kg IM twice daily | IV, IM | twice daily | 2-3 days | 🌎 NA |
| Polioencephalomalacia | 10-20 mg/kg | IM or SC | 3 times daily | — | 🌎 NA |
| Polioencephalomalacia | 10 mg/kg | IV, IM | up to 4 times a day | — | 🌎 NA |
| Adjunctive therapy of lead poisoning | 2 mg/kg | IM | Not specified | — | 🌎 NA |
- Polioencephalomalacia: If no improvement within 4 days, may be advisable to recommend slaughter.
- Polioencephalomalacia: If giving IV dilute in isotonic saline or isotonic dextrose.
- Polioencephalomalacia: First dose may be given via slow IV and subsequent doses IM. Severely affected animals may benefit from corticosteroids and mannitol.
- Adjunctive therapy of lead poisoning: Given at same time as CaEDTA therapy; total daily dose 8 mg/kg
Swine
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Thiamine deficiency | 5-100 mg | IM, SC, or IV | Not specified | — | 🌎 NA |
- Thiamine deficiency: Depending on formulation
Sheep
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Polioencephalomalacia | Initially, 10 mg/kg IV; then, 10 mg/kg IM twice daily | IV, IM | twice daily | 2-3 days | 🌎 NA |
| Thiamine deficiency | 20-200 mg | IM, SC, or IV | Not specified | — | 🌎 NA |
- Polioencephalomalacia: If no improvement within 4 days, may be advisable to recommend slaughter.
- Thiamine deficiency: Depending on formulation
Goats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Polioencephalomalacia | Initially, 10 mg/kg IV; then, 10 mg/kg IM twice daily | IV, IM | twice daily | 2-3 days | 🌎 NA |
- Polioencephalomalacia: If no improvement within 4 days, may be advisable to recommend slaughter.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Thiamine (Vitamin B1) is a water-soluble vitamin essential for carbohydrate metabolism and normal neurologic function.
Key Clinical Points:
- Deficiency Causes: In small animals, deficiency typically results from inadequate dietary intake (e.g., unsupplemented all-meat diets, heat-destroyed commercial diets) or ingestion of thiaminase-containing foods (e.g., raw fish). In ruminants, it is often secondary to thiaminase-producing rumen bacteria or ingestion of thiaminase-containing plants like bracken fern, leading to polioencephalomalacia (PEM).
- Clinical Signs: Manifests as gastrointestinal issues (anorexia, salivation), severe neuromuscular/CNS signs (ataxia, seizures, ventroflexion of the neck in cats, loss of reflexes), or cardiac arrhythmias.
- Adjunctive Uses: Frequently utilized in the management of ethylene glycol toxicity (to shunt metabolism away from toxic oxalates) and lead poisoning.
- Clinical Pearl: Because the brain relies heavily on carbohydrate metabolism, the CNS is highly sensitive to thiamine deficiency, making rapid supplementation critical when neurologic signs appear.
Mechanism of action
Thiamine is actively transported into cells where it combines with adenosine triphosphate (ATP) to form thiamine diphosphate (thiamine pyrophosphate or TPP).
- Enzymatic Co-factor: TPP is an essential coenzyme for several key metabolic enzymes, including pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase (both critical for the Krebs cycle/aerobic energy production), and transketolase (pentose phosphate pathway).
- Metabolic Pathway: Glucose → Pyruvate. Without TPP, pyruvate cannot be converted into acetyl-CoA.
- Pathophysiology of Deficiency: Diminished NADH production forces the cell into anaerobic glycolysis, converting accumulated pyruvic acid into lactic acid → Lactic acidosis and cellular energy failure (especially in high-demand tissues like the brain and heart).
Safety & warnings
Contraindications
- Known hypersensitivity to thiamine or any of its components
Adverse effects
- Hypersensitivity or anaphylactic reactions (rare)
- Vasovagal anaphylactic response in cats (cardiac arrest, severe bradycardia, apnea, hypotension, collapse) when given SC (rare)
- Injection site tenderness or muscle soreness (IM)
- Pain at the injection site (IM/SC)
- Anaphylaxis or hypersensitivity reactions (primarily with rapid IV administration)
Precautions
Anaphylaxis Warning: Hypersensitivity reactions, though rare, can occur. A severe vasovagal anaphylactic response has been noted in a small number of cats following subcutaneous administration.
- Administration: Intravenous administration should be performed slowly or diluted in fluids to minimize adverse cardiovascular reactions.
- Laboratory Interference: May cause false-positive serum uric acid results (phosphotungstate method) and urobilinogen urine spot tests (Ehrlich's reagent). Large doses may interfere with theophylline concentration assays (Schack and Wexler method).
Drug interactions
Thiamine may enhance the activity of neuromuscular blocking agents; clinical significance is unknown.
Monitoring
- Clinical efficacy (resolution of neurologic, gastrointestinal, or cardiac signs)
- Electrolyte levels (potassium, phosphate, magnesium) if treating conditions like feline hepatic lipidosis
- Resolution of clinical signs of thiamine deficiency (e.g., neurological improvement)
- Dietary intake and nutritional balance
Pharmacokinetics
Half-life
Absorption
Thiamine is readily absorbed from the gastrointestinal tract.
Distribution
Widely distributed to most body tissues.
Metabolism
Metabolized by the liver.
Elimination
Elimination is primarily renal, with the majority of the drug eliminated as metabolites.
Overdose
Very large doses of thiamine in laboratory animals have been associated with neuromuscular or ganglionic blockade, though the clinical significance in veterinary patients is unknown.
- Massive Doses: May cause hypotension and respiratory depression.
- Lethal Dose: A lethal dose of 350 mg/kg has been reported.
- Treatment: Generally, no specific treatment is required for most overdoses due to its water-soluble nature and rapid renal excretion.
Available products
Formulations
- Injection: 100 mg/mL, 200 mg/mL, 500 mg/mL
- Tablets: 50 mg, 100 mg, 250 mg
- Enteric Coated Tablets: 20 mg
- Oral Powder/Crumbles/Supplement
- Injectable: 100 mg/ml solution
- Oral: various tablets, capsules, and liquids
Veterinary
- Thiamine HCl for Injection: 200 mg/mL in 100 mL and 250 mL vials
- Thiamine HCl for Injection: 500 mg/mL in 100 mL vials
- Thiamine HCl Dietary Supplement: 8,200 mg per lb (Horse Care Durvit B-1 Crumbles)
- Thiamine HCl Supplement: 500 mg/oz (Thia-Dex, Vitamin B-1 Powder)
- 100 mg/ml injectable solution (authorized for farm animals)
Human-labeled
- Thiamine Tablets: 50 mg, 100 mg & 250 mg
- Thiamine Enteric Coated Tablets: 20 mg (Thiamilate)
- Thiamine HCl Injection: 100 mg/mL in 1 mL and 2 mL vials
- Various oral supplements (tablets, capsules)
Regulatory status
Withdrawal times: cattle meat 0 days · cattle milk 0 hours
Injectable formulations are authorized for veterinary use in farm animals (POM-V). Oral forms are widely available on general sale.
Withdrawal times: cattle meat 0 days · cattle milk 0 hours
Injectable formulations are POM-V (authorized for farm animals), while various oral formulations are available on general sale.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Protect from light and store at temperatures less than 40°C (preferably between 15-30°C); avoid freezing. Thiamine HCl is unstable in alkaline or neutral solutions, or with oxidizing/reducing agents. It is most stable at a pH of 2.
Client information
- Dietary Management: Ensure your pet is eating a balanced, commercially prepared diet. Avoid feeding raw fish or exclusively raw meat diets, as these can destroy thiamine and lead to severe deficiency.
- Administration: If your pet is prescribed thiamine, give it exactly as directed by your veterinarian. Do not skip doses.
- Observation: Contact your veterinarian immediately if you notice signs of weakness, stumbling, seizures, or if your cat's head drops down toward its chest (ventroflexion).
- Investigation: An epidemiologic investigation into the cause of the deficiency (diet, access to certain plants, raw fish) should be performed to prevent recurrence.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.