碘塞羅寧鈉
碘塞羅寧鈉（Liothyronine sodium）是**T3（三碘甲狀腺原氨酸）**的合成形式，即甲狀腺激素的活性細胞形式。 雖然左旋甲狀腺素（T4）是甲狀腺機能低下的標準第一線治療藥物，但碘塞羅寧保留用於對T4補充無反應的特定病例。這種無反應可能是由於胃腸道對T4的吸收不良，或理論上T4經脫碘酶轉化為T3的周邊轉化過程存在缺陷。 **臨床要點：** * 與左旋甲狀腺素相比，碘塞羅寧的**作用時間和半衰期短得多**，因此需要更頻繁地給藥（通常為一天三次）。 * **不建議將其用於初始治療**，因為它只能使血清T3濃度正常化，而T4水平仍然很低，這會破壞正常的下丘腦-垂體-甲狀腺反饋軸。 * 因為它繞過了身體自然的調節轉化步驟（T4 → T3），病患發生醫源性甲狀腺毒症的風險較高。
作用機制: Thyroid hormones act primarily at the cellular level to regulate metabolism. * **Mechanism:** T3 enters the cell and binds to **nuclear thyroid hormone receptors (TRs)** → the receptor-hormone complex binds to DNA → stimulates or inhibits the transcription of specific mRNA → alters protein synthesis. * **Physiologic Effects:** Increases the metabolic rate of tissues, enhances oxygen consumption, increases body temperature, stimulates gluconeogenesis, and promotes the mobilization and utilization of glycogen stores. * **Cardiovascular Effects:** Increases heart rate, cardiac output, and blood volume by upregulating beta-adrenergic receptors. * **Development:** Crucial for the adequate development of the central nervous system and skeletal growth.
各物種劑量
- Hypothyroidism · 4.4 micrograms/kg PO 2-3 times a day · PO · q8h-q12h
- T3 suppression test (diagnostic for hyperthyroidism) · 25 μg · PO · q8h · 7 doses total · Administer 7 doses, then measure T4 and T3 on the morning of the 3rd day, 2-4 hours after the 7th dose.
- Hypothyroidism (unresponsive to T4) · 4-6 micrograms/kg PO q8h · PO · q8h · Some dogs may require less frequent dosing. Only indicated when T4 supplementation has failed.
- Hypothyroidism (refractory to T4) · 4-6 μg/kg · PO · q8h · Not recommended as first-line therapy due to short half-life.
劑量為合格獸醫專業人員的臨床參考。請務必對照最新藥品仿單及個別病患確認。
給藥途徑
禁忌症
- Acute myocardial infarction
- Thyrotoxicosis
- Untreated adrenal insufficiency
- Untreated adrenal insufficiency (Addison's disease)
不良反應
- Tachycardia
- Polyphagia
- Polyuria/Polydipsia (PU/PD)
- Excitability
- Nervousness
- Excessive panting
- Apathy or listlessness (seen in about 10% of cats)
- PU/PD (Polyuria/Polydipsia)
- Nervousness/Anxiety
- Panting
- Weight loss
藥物相互作用
- Tricyclic/Tetracyclic Antidepressants · Increased risk for CNS stimulation and cardiac arrhythmias.
- Antidiabetic Agents (insulin, oral agents) · Thyroid hormones may increase the requirements for insulin or oral antidiabetic agents.
- Cholestyramine · May reduce liothyronine absorption; separate doses by at least 4 hours.
- Sympathomimetic Agents (epinephrine, norepinephrine) · Thyroid hormones can potentiate the cardiovascular effects of sympathomimetics.
- Warfarin · Thyroid hormones increase the catabolism of vitamin K-dependent clotting factors, potentially increasing anticoagulation effects.
- Digoxin · Potential for reduced digoxin levels and decreased therapeutic effect.
- Ketamine · Concurrent use may cause tachycardia and hypertension. · moderate
- Sympathomimetics · Increased risk of cardiac arrhythmias and coronary insufficiency · moderate
- Insulin · May alter glucose control, requiring dosage adjustments · minor
監測
- Serum T3 levels (draw just prior to dosing and 2-4 hours post-pill)
- Clinical signs of hyperthyroidism/thyrotoxicosis
- Note: Serum T4 levels will remain low during therapy
- Serum T3 levels
- Clinical signs of hyperthyroidism
- Heart rate and rhythm
過量
**Chronic Overdosage:** Produces signs of iatrogenic hyperthyroidism, including tachycardia, polyphagia, PU/PD, excitability, nervousness, and excessive panting. Some cats (approx. 10%) may exhibit 'apathetic' hyperthyroidism (listlessness, anorexia). **Treatment:** Reduce dosage or temporarily withhold until signs subside. **Acute Massive Overdosage:** Can produce signs resembling a **thyroid storm**. * **Treatment:** If oral ingestion is recent, reduce absorption using standard protocols (emetics, gastric lavage, activated charcoal, cathartics) unless contraindicated by the patient's clinical status. * **Supportive Care:** Oxygen, artificial ventilation, beta-blockers (e.g., propranolol) for tachycardia/arrhythmias, IV fluids, dextrose, and antipyretic agents as needed.
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