Thyrotropin (Thyroid Stimulating Hormone)
Thyrotropin (TSH) is a glycoprotein hormone used in veterinary medicine principally as a **diagnostic agent** in the TSH stimulation test to diagnose primary hypothyroidism. * **Historical Use:** Formerly available as a bovine-source veterinary product (Dermathycin®) for treating acanthosis nigricans and temporary supportive therapy in hypothyroidism. * **Current Practice:** The commercially available product is now derived from human sources via DNA recombinant technology (rhTSH). It is highly purified and preferred over older animal-derived products due to better availability and standardized potency. * **Clinical Pearl:** The TSH stimulation test is considered the gold standard for evaluating thyroid reserve and confirming a diagnosis of hypothyroidism when basal T4 and endogenous canine TSH concentrations are equivocal.
กลไกการออกฤทธิ์: Thyrotropin binds to **TSH receptors** on the basolateral membrane of thyroid follicular cells. This binding activates the **adenylate cyclase/cAMP pathway**, which stimulates multiple steps in thyroid hormone synthesis: * Increases **iodine uptake** (trapping) by the thyroid gland. * Stimulates the iodination of tyrosine residues on thyroglobulin. * Increases the production and secretion of active thyroid hormones (**T3 and T4**) into the systemic circulation. > With prolonged use, hyperplasia of thyroid cells may occur, though this is not a concern with single-dose diagnostic use.
ขนาดยาตามชนิดสัตว์
- TSH stimulation test · 25 μg/cat · IV · single dose · 1 day · The diagnostic value in cats has not been fully assessed.
- TSH stimulation test · 1 Unit/kg · IM · Once · Draw pre-dose baseline sample. Collect sample for T4 6 hours after dose.
- TSH stimulation test · 75 micrograms (total dose) · IV · Once · Blood samples taken before and 6 hours after rhTSH administration for determination of total serum thyroxine (T4) concentration.
- TSH stimulation test · 50-100 micrograms (0.05-0.1 mg) · IV · Once · Measure serum T4 at 0 hours (pre-sample) and 4 hours post. Product may be frozen for at least 8 weeks with no loss of potency.
- TSH stimulation test · 50-150 μg/dog · IV · single dose · 1 day · Higher doses offer increased discriminatory power in dogs with comorbidities or those receiving thyroid-suppressing drugs.
ขนาดยาเป็นข้อมูลอ้างอิงทางคลินิกสำหรับสัตวแพทย์ผู้มีใบอนุญาต โปรดตรวจสอบกับฉลากล่าสุดและผู้ป่วยแต่ละรายเสมอ
วิธีการให้ยา
ข้อห้ามใช้
- Adrenocortical insufficiency (untreated Addison's disease)
- Hyperthyroidism
- Coronary thrombosis
- Hypersensitivity to bovine thyrotropin or human proteins
- Repeated administration is not advisable
- Patients currently receiving levothyroxine therapy
- Use of chemical grade TSH (due to anaphylaxis risk)
อาการไม่พึงประสงค์
- Hypersensitivity reactions (especially with repeated injections of human-derived proteins in animals)
- Clinical signs of hyperthyroidism (with chronic administration or high doses)
- Anaphylactic responses (specifically associated with chemical grade/bovine TSH; recombinant forms are generally well tolerated)
อันตรกิริยาระหว่างยา
- Anabolic or androgenic steroids · May decrease serum T4 levels, making the TSH stimulation test hard to interpret · moderate
- Carbimazole · May decrease serum T4 levels, making the TSH stimulation test hard to interpret · moderate
- Barbiturates · May decrease serum T4 levels, making the TSH stimulation test hard to interpret · moderate
- Corticosteroids · May decrease serum T4 levels, making the TSH stimulation test hard to interpret · moderate
- Diazepam · May decrease serum T4 levels, making the TSH stimulation test hard to interpret · moderate
- Heparin · May decrease serum T4 levels, making the TSH stimulation test hard to interpret · moderate
- Mitotane · May decrease serum T4 levels, making the TSH stimulation test hard to interpret · moderate
- Phenylbutazone · May decrease serum T4 levels, making the TSH stimulation test hard to interpret · moderate
- Phenytoin · May decrease serum T4 levels, making the TSH stimulation test hard to interpret · moderate
- Salicylates · May decrease serum T4 levels, making the TSH stimulation test hard to interpret · moderate
- Fluorouracil · May cause T4 levels to be increased, making the TSH stimulation test hard to interpret · moderate
การติดตาม
- Serum total T4 concentrations (baseline and 4-6 hours post-administration)
- Clinical signs of hypersensitivity or anaphylaxis during and immediately after administration
- Serum total T4 levels (baseline and post-stimulation, typically 4-6 hours post-injection)
การได้รับยาเกินขนาด
Chronic administration at high dosages can produce clinical signs of **hyperthyroidism** (e.g., weight loss, polyphagia, tachycardia, hyperactivity). Massive overdoses can cause clinical signs resembling **thyroid storm** (a life-threatening hypermetabolic state). Treatment is generally supportive and symptomatic; refer to levothyroxine overdose protocols for specific management strategies.
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