レボチロキシン
レボチロキシン（l-チロキシンまたはT4）は、天然の甲状腺ホルモンであるチロキシンの合成形態です。獣医学における**甲状腺機能低下症**の治療の第一選択薬です。 > **臨床上の警告：** 既存の心疾患がある患者では、過度の心刺激を防ぐため、初期用量を低く設定する必要があります。また、自己免疫性多内分泌腺症候群の患者においてアジソン病を顕在化させる可能性があります。
作用機序: Levothyroxine acts as a replacement for endogenous thyroxine. It enters cells and is converted to the more active T3 (triiodothyronine). T3 then **binds to specific intracellular thyroid hormone receptors** in the nucleus → **alters gene expression** → regulates metabolism, growth, and development.
動物種別の用量
- Hypothyroidism · 0.02-0.04 mg/kg/day OR 0.5 mg/m2 body surface area daily · PO · sid or divided bid · Lifelong · Dose given with food. Monitor serum T4 levels pre-dosing and 4-8 hours after dosing.
- Hypothyroidism · 0.02-0.04 mg/kg/day OR 0.5 mg/m2 body surface area daily · PO · sid or divided bid · Lifelong · Dose given with food. Monitor serum T4 levels pre-dosing and 4-8 hours after dosing.
用量は獣医療従事者向けの臨床リファレンスです。必ず最新の添付文書と個々の患者で確認してください。
投与経路
禁忌
- Uncorrected adrenal insufficiency (Addison's disease)
- Acute myocardial infarction (general precaution)
有害事象
- Tachycardia
- Excitability
- Nervousness
- Excessive panting
- Unmasking of Addison's disease
薬物相互作用
- Catecholamines · Actions of catecholamines are enhanced by thyroxine · moderate
- Sympathomimetics · Actions of sympathomimetics are enhanced by thyroxine · moderate
- Insulin · Altered insulin requirements; monitor carefully during initiation of therapy · moderate
- Oestrogens · May increase thyroid requirements by increasing thyroxine-binding globulin · moderate
- Ciclosporin · Therapeutic effect may be reduced by thyroid hormones · moderate
- Digoxin · Therapeutic effect may be reduced by thyroid hormones · moderate
- Digitoxin · Therapeutic effect may be reduced by thyroid hormones · moderate
- Ketamine · Tachycardia and hypertension may develop when given to patients receiving thyroid hormones · major
モニタリング
- Serum total T4 levels (pre-pill trough and 4-8 hours post-pill peak)
- Clinical response (resolution of lethargy, weight gain, dermatological signs)
- Signs of thyrotoxicosis (panting, tachycardia, hyperactivity)
- Blood glucose in diabetic patients
過量投与
Clinical signs of overdosage (thyrotoxicosis) include **tachycardia**, **excitability**, **nervousness**, and **excessive panting**. Treatment involves withholding the medication until signs resolve, then restarting at a lower dose. Acute massive overdose may require gastrointestinal decontamination and supportive care (e.g., beta-blockers for severe tachycardia).
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。