Methimazole 甲狀腺機能亢進

Methimazole
台灣的商品~ 利甲錠LICA Tablets; 平甲錠(Antiroid Tablets) ; Tapazole(Thimazol) 甲美樂糖衣錠 5mg/tab

注意事項: 孕婦需慎用，哺乳期間請勿使用此藥品

利甲錠仿單註明：懷孕期間使用最小的有效劑量，且儘可能於分娩前 2-3 週停藥，

methimazole具有肝毒性, 若肝指數超過三倍需停用. 

methimazole 初始劑量是每天 15~30 mg分三次使用.  1#-2# tid.
可搭配 beta blocker 使用
beta blocker 使用 4-8 周之後可以慢慢減量
根據臨床症狀與每個月甲狀腺素檢驗, 將 methimazole 調低劑量, 最後維持劑量 5-10 mg QD.

不能根據TSH評估療效
過多的T3.T4會抑制 TSH 分泌, 但 T3 T4 降低之後, TSH 可能數個月內仍過低而測不到, 所以不能根據 TSH 濃度評估療效.

甲狀腺亢進停藥條件
治療一年之後,
.... 抗甲狀腺藥物治療時間通常是 1-2 年. 有研究說, 使用半年就停藥的復發機率較高
甲狀腺濃度正常.
沒有臨床症狀,
促甲狀腺分泌抗體 TSI 已經無法測得

停藥後至少追蹤甲狀腺功能3年 (第一年隔3~6個月，以後每隔6~12個月追蹤一次)。
如果 TSI 濃度上升, 應考慮再治療一年.
停用甲亢藥物之後, 應追蹤甲狀腺素, 甲亢症復發通常是在停藥第一年內
第一年, 每三個月抽血一次
之後每年抽血一次
甲亢症在停藥數年後仍可能發生
再發之後, 建議使用放射性碘, 或者手術治療, 也可以再次服用抗甲狀腺藥物

服用抗甲狀腺藥物可能有 0.2%-0.5% 機率發生顆粒球減少. 顆粒球包括: neutrophil, eosinophil, basophil, 用藥三個月內最容易發生, 如果 PMN < 1500 應停用藥物. 視情況隔離或用抗生素治療, 停藥後通常兩周左右, 白血球會慢慢恢復.

Neutrophils 佔白血球總數的 50%-60%, 所以臨床上常說 neutropenia ,

(Thyroid stimulating immunoglobulin (TSI): A form of immunoglobulin G (IgG) that can bind to thyrotropin (TSH) receptors on the thyroid gland. TSIs mimic the action of TSH, causing excess secretion of thyroxine and triiodothyronine. The TSI level is abnormally high in persons with hyperthyroidism due to Graves' disease.)

Methimazole usually is the drug of choice in nonpregnant patients because of its lower cost, longer half-life, and lower incidence of hematologic side effects. The starting dosage is 15 to 30 mg per day, and it can be given in conjunction with a beta blocker.28 The beta blockade can be tapered after four to eight weeks and the methimazole adjusted, according to clinical status and monthly free T4 or free T3 levels, toward an eventual euthyroid (i.e., normal T3 and T4 levels) maintenance dosage of 5 to 10 mg per day. TSH levels may remain undetectable for months after the patient becomes euthyroid and should not be used to monitor the effects of therapy. At one year, if the patient is clinically and biochemically euthyroid and a thyroid-stimulating antibody level is not detectable, therapy can be discontinued. If the thyroid-stimulating antibody level is elevated, continuation of therapy for another year should be considered. Once antithyroid drug therapy is discontinued, the patient should be monitored every three months for the first year, because relapse is more likely to occur during this time, and then annually, because relapse can occur years later. If relapse occurs, radioactive iodine or surgery generally is recommended, although antithyroid drug therapy can be restarted.

參考資料
亞臨床型甲狀腺機能亢進~ 家庭醫學與基層醫療   第三十卷 第十二期
甲狀腺機能亢進的處理原則 鄭高奇1 賴世偉2 林正介3