チアミン (ビタミンB1)
チアミン（ビタミンB1）は、炭水化物代謝および正常な神経機能に不可欠な水溶性ビタミンです。 **主な臨床的ポイント：** * **欠乏の原因：** 小動物では、通常、食事からの摂取不足（サプリメント無添加の全肉食、加熱により破壊された市販食など）や、チアミナーゼを含む食品（生魚など）の摂取によって生じます。反芻動物では、チアミナーゼを産生するルーメン細菌や、ワラビなどのチアミナーゼを含む植物の摂取に続発することが多く、**大脳皮質壊死症（PEM）**を引き起こします。 * **臨床症状：** 胃腸症状（食欲不振、流涎）、重度の神経筋/中枢神経系症状（運動失調、発作、猫の頸部腹側屈曲、反射消失）、または不整脈として現れます。 * **補助的用途：** **エチレングリコール中毒**（毒性のあるシュウ酸塩の生成を避けるための代謝経路の変更）および**鉛中毒**の管理に頻繁に使用されます。 * **臨床のヒント：** 脳は炭水化物代謝に大きく依存しているため、中枢神経系はチアミン欠乏に対して非常に敏感であり、神経症状が現れた場合は迅速な補充が不可欠です。
作用機序: 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).
動物種別の用量
- 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
投与経路
禁忌
- Known hypersensitivity to thiamine or any of its components
- Known hypersensitivity to thiamine
有害事象
- 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)
薬物相互作用
- Neuromuscular blocking agents · Thiamine may enhance the activity of neuromuscular blocking agents; clinical significance is unknown. · minor
モニタリング
- 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
過量投与
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.
VetSheet の薬剤リファレンスは、獣医療従事者向けの臨床意思決定支援を目的としており、専門的判断やメーカーの最新添付文書に代わるものではありません。