左旋甲狀腺素鈉
Levothyroxine Sodium
3,5,3',5'-tetra-iodo-L-thyronine sodium
別名: Soloxine · Synthroid · Levosyn · Thyro-Tabs · Thyrosyn · Leventa · Thyro-L · Levothroid · Levoxyl · Tirosint · T4 thyroxine sodium · levothyroxin natrium · levothyroxinum natricum · L-thyroxine sodium · tirossina · tiroxina sodica
由 VetSheet 獸醫團隊審訂更新於 2026年4月5日本內容以實證獸醫文獻為本
劑量為合格獸醫專業人員的臨床參考。請務必對照最新仿單及個別病患確認。
各物種劑量
🌎 NA — North America🌍 EU — Europe
狗
| 適應症 | 劑量 | 途徑 | 頻次 | 療程 | 地區 |
|---|---|---|---|---|---|
| Hypothyroidism | 20 micrograms/kg (0.02 mg/kg) body weight PO twice daily with a maximum dose of 0.8 mg twice daily | PO | q12h | — | 🌎 NA |
| Hypothyroidism | 10-22 micrograms/kg q12h or q24h | PO | q12h or q24h | — | 🌎 NA |
| Hypothyroidism | 0.02 mg/kg PO twice daily to start; (0.02-0.04 mg/kg PO once daily or, if necessary divided twice daily to maintain). Alternatively, give 0.5 mg/m2 | PO | q12h or q24h | — | 🌎 NA |
| Myxedema coma | 5 micrograms/kg IV q12h initially | IV | q12h | — | 🌎 NA |
- Hypothyroidism: Evaluate clinical response 4-8 weeks later and draw a T4 level 4-6 hours post dosing.
- Hypothyroidism: Maximum of 0.8 mg q12h. Reevaluate 1-2 months after initiating therapy.
- Hypothyroidism: 0.5 mg/m2 dosing may prevent hyperthyroid effects, particularly in large breed dogs.
- Myxedema coma: Oral administration may be poorly absorbed in this state.
貓
| 適應症 | 劑量 | 途徑 | 頻次 | 療程 | 地區 |
|---|---|---|---|---|---|
| Hypothyroidism | 0.05-0.1 mg per cat PO once daily | PO | q24h | — | 🌎 NA |
| Post thyroidectomy | 0.1-0.2 mg (total dose) PO once daily beginning 24-48 hours post-op | PO | q24h | Several weeks or months | 🌎 NA |
- Hypothyroidism: Wait a minimum of 4-6 weeks to assess clinical response.
- Post thyroidectomy: Monitor T4 levels to determine when supplementation can be ceased.
鳥
| 適應症 | 劑量 | 途徑 | 頻次 | 療程 | 地區 |
|---|---|---|---|---|---|
| Hypothyroidism | One 0.1 mg tablet in 30 mL-120 mL of water daily | PO | q24h | — | 🌎 NA |
- Hypothyroidism: Stir water and offer for 15 minutes and remove. Use high dose for budgerigars and low dose for water drinkers.
爬蟲類
| 適應症 | 劑量 | 途徑 | 頻次 | 療程 | 地區 |
|---|---|---|---|---|---|
| Hypothyroidism in tortoises | 0.02 mg/kg PO every other day | PO | q48h | — | 🌎 NA |
馬
| 適應症 | 劑量 | 途徑 | 頻次 | 療程 | 地區 |
|---|---|---|---|---|---|
| Hypothyroidism | 10 mg in 70 mL of corn syrup once daily | PO | q24h | — | 🌎 NA |
| Adjunctive treatment of equine metabolic syndrome | 0.1 mg/kg PO once daily, initiate treatment at 48 mg/day... and then increase to 72 mg/day after 3 months if the horse remains obese | PO | q24h | 6 months | 🌎 NA |
- Hypothyroidism: Monitor T4 levels one week after initiation of therapy.
- Adjunctive treatment of equine metabolic syndrome: Taper off by administering 24 mg/day for 2 weeks and then 12 mg/day for 2 weeks.
劑量為合格獸醫專業人員的臨床參考。請務必對照最新仿單及個別病患確認。
概覽
左旋甲狀腺素鈉是甲狀腺分泌的內源性激素甲狀腺素 (T4) 的合成左旋異構體。它被認為是獸醫學中甲狀腺激素替代療法的黃金標準，主要用於治療犬隻的甲狀腺機能低下症，偶爾也用於其他物種。
臨床重點：
- 前驅激素特性： T4 主要是一種前驅激素，在周邊組織中會轉化為生物活性更強的 T3。
- 生物利用度： 個體動物的口服吸收率差異很大，且可能受食物影響。通常建議空腹給藥以確保吸收一致。
- 治療監測： 由於個體藥代動力學的差異，必須進行血清總 T4 (TT4) 的治療藥物監測 (TDM)，以針對個別病患調整劑量。
作用機轉
Thyroid hormones regulate multiple metabolic processes, including fat, protein, and carbohydrate metabolism, and are critical for normal growth, development, and basal metabolic rate.
- Pathway: Exogenous levothyroxine (T4) is absorbed and distributed to peripheral tissues.
- Conversion: Inside cells, T4 is enzymatically deiodinated by 5'-deiodinase to triiodothyronine (T3), the primary active hormone.
- Receptor Binding: T3 enters the nucleus and binds to thyroid hormone receptors (TRs).
- Gene Transcription: The TR-T3 complex binds to thyroid response elements (TREs) on DNA → alters gene transcription → increases mRNA synthesis → increases protein synthesis, oxygen consumption, heart rate, and cellular metabolism.
安全性與警告
禁忌症
- Acute myocardial infarction
- Thyrotoxicosis
- Untreated adrenal insufficiency
不良反應
- Tachycardia
- Polyphagia
- Polyuria/Polydipsia (PU/PD)
- Excitability
- Nervousness
- Excessive panting
- Apathy or listlessness (seen in some cats)
注意事項
Use with caution and at a lower initial dosage in patients with concurrent hypoadrenocorticism (treated), cardiac disease, diabetes, or in elderly patients. High fiber diets may reduce absorption. Hypothyroid dogs can have decreased GFR; restoration to a euthyroid state can increase GFR and reduce serum creatinine levels. Numerous drugs can affect thyroid function tests (T4, T3, TSH), so evaluate lab results accordingly.
藥物交互作用
May decrease the metabolism of T4 to T3
May reduce levothyroxine absorption; separate doses by 4 hours
Increased risk for CNS stimulation and cardiac arrhythmias
Levothyroxine may increase requirements for insulin or oral agents
May reduce levothyroxine absorption; separate doses by 4 hours
Decreased conversion of T4 to T3
Potential for reduced digoxin levels
May reduce levothyroxine absorption; separate doses by 4 hours
May cause tachycardia and hypertension
Possible increased metabolism of thyroxine; dosage adjustments may be needed
Decreased conversion of T4 to T3
Possible increased metabolism of thyroxine; dosage adjustments may be needed
May increase levothyroxine requirements
May reduce levothyroxine absorption; separate doses by 4 hours
Levothyroxine can potentiate effects
Thyroid hormones increase the catabolism of vitamin K-dependent clotting factors that may increase the anticoagulation effects
監測
- Clinical signs of resolution of hypothyroidism (e.g., improved energy, hair regrowth, weight loss)
- Signs of thyrotoxicosis/hyperthyroidism (tachycardia, panting, weight loss with polyphagia)
- Serum total T4 (TT4) levels (typically measured 4-6 hours post-pill for peak levels)
- Canine TSH (cTSH) if indicated
藥物動力學
半衰期
吸收
Wide variability from animal to animal.
代謝
Converted in peripheral tissues from T4 to T3.
過量
Chronic overdosage will produce signs of hyperthyroidism, including tachycardia, polyphagia, PU/PD, excitability, nervousness, and excessive panting. Some cats (approx. 10%) may exhibit 'apathetic' hyperthyroidism (listlessness, anorexia).
- Management of Chronic OD: Reduce dosage and/or temporarily withhold until signs subside.
- Acute Overdose: Less likely to cause severe thyrotoxicosis than chronic OD. Signs may include vomiting, diarrhea, hyperactivity to lethargy, hypertension, tachycardia, tachypnea, dyspnea, and abnormal pupillary light reflexes. In dogs, signs appear within 1-9 hours.
- Treatment of Acute OD: If ingestion occurred within 2 hours, use standard decontamination protocols (emetics, cathartics, activated charcoal). Provide supportive care (oxygen, artificial ventilation, beta-blockers like propranolol, fluids, dextrose, antipyretics).
可用產品
劑型
- Chewable tablets
- Oral solution
- Injection (lyophilized powder)
- Liquid-filled oral capsules
獸醫用
- Levothyroxine Sodium Tablets: 0.1 mg, 0.2 mg, 0.3 mg, 0.4 mg, 0.5 mg, 0.6 mg, 0.7 mg, 0.8 mg, 1 mg (Soloxine, Levosyn, Thyro-Tabs, Thyrosyn, Thyroxine-L, Thyrozine, Thyrokare)
- Levothyroxine Sodium Tablets Chewable: 0.1 mg to 0.8 mg (Canine Thyroid Chewable Tablets, Nutrived T-4, Heska Thyromed)
- Levothyroxine Oral Solution: 1 mg/mL (Leventa)
- Levothyroxine Sodium Powder: 0.22% (Equine Thyroid Supplement, Thyrozine Powder, Levoxine Powder, Thyro-L, Throxine-L Powder, Equi-Phar Thyrosyn Powder, Thyrokare Powder)
人用標示
- Levothyroxine Sodium Tablets: 0.025 mg to 0.3 mg (Synthroid, Levothroid, Levoxyl, Unithroid)
- Levothyroxine Sodium Liquid-filled Oral Capsules: 13 mcg to 150 mcg (Tirosint)
- Levothyroxine Powder for Injection lyophilized: 200 mcg & 500 mcg
各地核准狀態
暫無法規資料: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
儲存與穩定性
Store at room temperature in tight, light-resistant containers. The injectable product should be reconstituted immediately before use; discard unused portions. Do not mix injection with other drugs or IV fluids. Aqueous solutions are reportedly unstable.
飼主須知
重要提示： 規律給藥是關鍵！請每天在同一時間給予此藥物，最好是空腹或固定搭配同一種食物，因為食物會影響藥物的吸收量。
- 終身治療： 甲狀腺機能低下通常是終身疾病。未經獸醫師同意，請勿自行停藥。
- 監測： 您的寵物需要定期進行血液檢查，以確保劑量完全正確。劑量太少無法改善症狀，太多則會引起副作用。
- 注意過量跡象： 如果您的寵物開始過度飲水或排尿、嚴重喘氣、表現出緊張或過度活躍，或者食慾極佳卻體重減輕，請立即聯繫您的獸醫師。
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