左旋甲狀腺素
左旋甲狀腺素（l-Thyroxine 或 T4）是一種合成的天然甲狀腺荷爾蒙。它是獸醫學中治療**甲狀腺機能低下症**的首選藥物。 > **臨床警告：** 患有潛在心臟疾病的病患在初期需要較低的劑量，以防止過度的心臟刺激。在患有自體免疫多發性內分泌腺綜合症的病患中，它也可能誘發愛迪生氏症（腎上腺皮質機能低下症）。
作用機制: 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.
各物種劑量
- 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.
劑量為持牌獸醫專業人員的臨床參考。請務必對照最新藥品說明書及個別病患確認。
給藥途徑
禁忌症
- Uncorrected adrenal insufficiency (Addison's disease)
- Acute myocardial infarction (general precaution)
不良反應
- Tachycardia
- Excitability
- Nervousness
- Excessive panting
- Unmasking of Addison's disease
藥物相互作用
- 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
監測
- 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
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 藥物參考供持牌獸醫專業人員作臨床決策輔助之用,不能取代專業判斷或廠方最新藥品說明書。