Thiamine (Vitamin B1)
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.
Mecanismo: 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).
Dosificación por especie
- Polioencephalomalacia · Initially, 10 mg/kg IV; then, 10 mg/kg IM twice daily · IV, IM · twice daily · 2-3 days · If no improvement within 4 days, may be advisable to recommend slaughter.
- Thiamine deficiency · 20-200 mg · IM, SC, or IV · Not specified · Depending on formulation
- Polioencephalomalacia · Initially, 10 mg/kg IV; then, 10 mg/kg IM twice daily · IV, IM · twice daily · 2-3 days · If no improvement within 4 days, may be advisable to recommend slaughter.
- Thiamine deficiency · 100-250 mg · parenterally · twice a day · Experimentally, as little as 1 mg is effective
- Thiamine deficiency · 10-20 mg/kg · IM · Not specified · for several days
- Adjunctive treatment of hepatic lipidosis · 100 mg of thiamine in one liter of crystalloid fluids · IV · Not specified · With additional soluble B vitamins. Indicated if neck ventroflexion is present.
- Thiamine deficiency · 100-250 mg · SC · twice daily · for several days until regression of symptoms with complete recovery
- 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
Vías de administración
Contraindicaciones
- Known hypersensitivity to thiamine or any of its components
- Known hypersensitivity to thiamine
Efectos adversos
- 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)
Interacciones farmacológicas
- Neuromuscular blocking agents · Thiamine may enhance the activity of neuromuscular blocking agents; clinical significance is unknown. · minor
Monitoreo
- 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
Sobredosis
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.
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