메티마졸

항갑상선제 (티오이미다졸 유도체)

**메티마졸(Methimazole)**은 티오이미다졸 유도체 항갑상선제로, 북미에서 **고양이 갑상선 기능 항진증의 내과적 치료를 위한 표준 치료제(Gold standard)**로 간주됩니다. 주요 임상 포인트: - **주요 용도**: 고양이 갑상선 기능 항진증 관리. 순환하는 갑상선 호르몬 수치를 효과적으로 낮추어 체중 감소, 다식증, 빈맥 등의 임상 증상을 해결합니다. - **대체 투여 경로**: 알약 투여가 어려운 고양이의 경우, 귓바퀴 안쪽에 바르는 **경피용 PLO 겔**로 조제할 수 있으며, 이는 경구 투여보다 약간 낮지만 좋은 임상적 효능을 보이고 위장관 부작용이 적을 수 있습니다. - **연구 목적 용도**: 개에서 시스플라틴(cisplatin)으로 인한 신독성을 예방하기 위해 정맥 주사로 사용된 바 있습니다. - **임상 팁**: 메티마졸은 갑상선 기능 항진증을 관리할 뿐 *완치시키지는 않습니다*. 근본적인 치료(방사성 요오드 또는 갑상선 절제술)를 받지 않는 한 평생 매일 투약해야 합니다.

작용 기전: Methimazole acts directly within the thyroid gland to block the synthesis of thyroid hormones (T3 and T4). - **Mechanism**: It actively inhibits the enzyme **thyroid peroxidase (TPO)**. - **Pathway**: Inhibition of TPO → prevents the oxidation of iodide to iodine → blocks the incorporation of iodine into tyrosyl residues of thyroglobulin → inhibits the coupling of iodinated tyrosyl residues to form iodothyronine (T3 and T4). - **Important Note**: Methimazole has **no effect** on the release or activity of thyroid hormones that are already formed and stored, or those currently in systemic circulation. This accounts for the **1 to 3 week lag time** often seen before serum T4 levels significantly decrease and clinical improvement is noted.

동물 종별 용량

Cats

Hyperthyroidism · The starting dose is 2.5 mg administered every 12 hours. Following 3 weeks of treatment, the dose should be titrated to effect based on individual serum total T4 (TT4) levels and clinical response. Dose adjustments should be made in 2.5 mg increments. The maximum total dosage is 20 mg per day divided, not to exceed 10 mg as a single administration. · PO · q12h · Lifelong
Hyperthyroidism (cats with azotemia or for clients declining radioiodine) · 1.25-5 mg per cat twice daily (start at lower end. · PO · q12h · Lifelong
Hyperthyroidism (transdermal administration) · 2.5 mg to inner pinna q12h. · topical · q12h · Lifelong · Methimazole (50 mg/mL; 5 mg/0.1 mL) in PLO. Person applying should wear gloves or finger cots. Somewhat lower efficacy than PO (67% vs 82% euthyroid at 4 weeks). Lower incidence of GI effects.
Hyperthyroidism (gradual titration) · Initially, 2.5 mg (total dose) PO once a day for 2 weeks. If adverse reactions not noted... increase to 2.5 mg PO twice daily and the same parameters are checked in another 2 weeks. The dosage should then be increased every 2 weeks by 2.5 mg per day until serum T4 is between 13 and 26 nmol/L or adverse effects develop. · PO · q24h initially, then q12h · Lifelong
Hyperthyroidism (based on renal status) · If no signs of renal insufficiency/failure, begin at 5 mg (total dose) PO twice daily in cases with severely increased T4 levels. If renal insufficiency present (or not sure), start at 2.5 mg twice daily. If azotemia and overt renal failure, start at 1.25 mg twice a day. · PO · q12h · Lifelong · Monitor in 1-2 weeks (T4, CBC with platelet count, renal blood parameters, urinalysis).
Hyperthyroidism · 2.5 mg/cat · PO · q12h · Long-term · 2 to 3 weeks of treatment generally needed to establish euthyroidism. Adjust dose based on T4 monitoring.

투여 경로

POtopicalIVTopical

금기

Hypersensitivity to methimazole, carbimazole, or polyethylene glycol
Autoimmune disease
Primary liver disease
Renal failure
Hematologic disorders or coagulopathies
Pregnant or lactating queens
Pregnant queens
Lactating queens
Animals with known hypersensitivity to thiamazole or carbimazole

이상반응

Vomiting
Anorexia
Depression/Lethargy
Transient eosinophilia, leukopenia, and lymphocytosis
Self-induced facial excoriations (pruritus)
Bleeding/Coagulopathies
Hepatopathy
Thrombocytopenia
Agranulocytosis
Positive direct antiglobulin test (DAT)
Positive ANA (in chronic use >6 months)
Acquired myasthenia gravis (rare)
Inappetence / Anorexia
Jaundice / Hepatopathy
Cytopenias (thrombocytopenia, leukopenia, anemia)
Immune-mediated diseases (e.g., myasthenia gravis)

약물 상호작용

Benzimidazole antiparasitics · Methimazole can reduce hepatic oxidation of benzimidazoles and increase blood levels.
Beta-blockers · A reduction in dose may be needed when the patient becomes euthyroid.
Bupropion · Potential for increased risk for hepatotoxicity; increased monitoring (LFT's) necessary.
Digoxin · Methimazole may decrease digoxin efficacy, but a reduction in dose may be needed when the patient becomes euthyroid.
Phenobarbital · Concurrent use of phenobarbital may reduce the clinical effectiveness of methimazole. · moderate
Theophylline · A reduction in dose may be needed when the patient becomes euthyroid.
Warfarin · Anticoagulants may be potentiated by methimazole. Increased monitoring of anticoagulant effect is warranted.
Benzimidazoles · Reduce hepatic oxidation and may lead to increased circulating thiamazole concentrations · moderate
Iodine-131 (Radioiodine) · Thiamazole interferes with radioiodine uptake; must be discontinued prior to I-131 treatment · major
Low-iodine prescription diets · Concurrent use is not recommended as it confounds dietary management and iodine restriction · moderate

모니터링

Baseline and every 2-3 weeks for the first 3 months: CBC, platelet count, Serum T4
Liver function tests and ANA if indicated by symptomatology
After stabilization (at least 3 months): T4 at 3-6 month intervals
Renal parameters (BUN, Creatinine, USG) to monitor for unmasked kidney disease
Cats receiving >10 mg/day require more frequent monitoring
Serum total T4 (measure 4-6 hours post-pill)
Haematology (CBC for cytopenias)
Biochemistry (BUN, Creatinine, Liver enzymes)
Monitor at 3, 6, 10, and 20 weeks after starting therapy, and every 3 months thereafter

과용량

Acute toxicity from overdosage mirrors severe adverse effects: **agranulocytosis, hepatopathy, and thrombocytopenia** are the most serious concerns. **Treatment**: - Follow standard protocols for oral ingestion (empty stomach if not contraindicated, administer activated charcoal). - Provide symptomatic and supportive care (e.g., IV fluids, hepatoprotectants, broad-spectrum antibiotics if neutropenic).

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