Drilldown: Medicines

Levothyroxine (1) · Liothyronine (T3, triiodothyronine sodium) (1)

Cytomel (oral), Triostat (IV) (1) · Synthroid, Levoxyl, Tirosint, Unithroid, Euthyrox (1)

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None (1) · Synthetic T4 (thyroxine); peripherally deiodinated to T3 (triiodothyronine), the active hormone. '"`UNIQ--vote-00000031-QINU`"' Narrow therapeutic index; brand-to-generic switches can shift TSH and require re-titration'"`UNIQ--ref-00000032-QINU`"'. (1)

'"`UNIQ--vote-00000033-QINU`"', '"`UNIQ--vote-00000034-QINU`"', '"`UNIQ--vote-00000035-QINU`"' (1) · '"`UNIQ--vote-0000149A-QINU`"', '"`UNIQ--vote-0000149B-QINU`"', '"`UNIQ--vote-0000149C-QINU`"' (1)

1.6 mcg/kg/d in young healthy adults; 25-50 mcg/d in elderly or cardiac disease, titrated by TSH at 6-8 weeks (1) · Hypothyroidism: 5-25 mcg PO daily (start low, titrate slowly); myxedema coma: 5-20 mcg IV q4-12h with T4 loading (1)

25, 50, 75, 88, 100, 112, 125, 137, 150, 175, 200, 300 mcg tablets; oral capsule and IV/IM also available (1) · 5, 25, 50 mcg tablets (Cytomel); 10 mcg/mL IV (Triostat) (1)

100 mcg/d typical (1) · No fixed maximum; titrated to TSH target (1)

None · Oral · IV · topical · IM · intranasal · rectal · Subcutaneous · topical ophthalmic · ophthalmic · intramuscular · intravenous · transdermal · vaginal · Subcutaneous (abdomen · sublingual · thigh · Inhaled · SC · intra-articular

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Hours (faster than T4); peak biologic activity 24-48 hours (1) · TSH normalization 4-8 weeks; symptomatic improvement weeks to months (1)

24-72 hours (1) · Steady-state at 4-6 weeks (1)

~1 day (much shorter than T4's ~7 days)'"`UNIQ--ref-0000149D-QINU`"' (1) · ~7 days (euthyroid); longer in hypothyroidism (~9-10 days), shorter in hyperthyroidism'"`UNIQ--ref-00000036-QINU`"' (1)

40-80% (oral); reduced by food, calcium, iron, PPIs, fiber; take fasting with water'"`UNIQ--ref-00000037-QINU`"' (1) · ~95% (oral)'"`UNIQ--ref-0000149E-QINU`"' (1)

First-line in pregnancy; dose typically increased 25-30% due to estrogen-driven rise in TBG and fetal demand. Lactation safe at physiologic doses.<sup class="pcp-cn" title="This claim needs a citation.">&#91;[[Pharmacopedia:Citation needed|citation&nbsp;needed]]&#93;</sup> (1) · T4 (levothyroxine) is the first-line in pregnancy; T3 is rarely needed.<sup class="pcp-cn" title="This claim needs a citation.">&#91;[[Pharmacopedia:Citation needed|citation&nbsp;needed]]&#93;</sup> (1)

[[USLegal:Prescription only|Rx-only]] in US (2)