Drilldown: Medicines
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generic:
brand:
classes:
mechanism:
None (3) ·
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-00000032-QINU`"' Brand-to-brand and lot-to-lot variability in T3:T4 ratio is greater than with synthetic levothyroxine, which is why endocrine guidelines prefer the synthetic'"`UNIQ--ref-00000033-QINU`"'. (1)
uses:
'"`UNIQ--vote-00000033-QINU`"', '"`UNIQ--vote-00000034-QINU`"', '"`UNIQ--vote-00000035-QINU`"' (1) ·
'"`UNIQ--vote-00000034-QINU`"', '"`UNIQ--vote-00000035-QINU`"' (1) ·
'"`UNIQ--vote-0000059A-QINU`"', '"`UNIQ--vote-0000059B-QINU`"' (1) ·
'"`UNIQ--vote-000005B3-QINU`"', '"`UNIQ--vote-000005B4-QINU`"', '"`UNIQ--vote-000005B5-QINU`"', '"`UNIQ--vote-000005B6-QINU`"' (1) ·
'"`UNIQ--vote-00000607-QINU`"', '"`UNIQ--vote-00000608-QINU`"', '"`UNIQ--vote-00000609-QINU`"', '"`UNIQ--vote-0000060A-QINU`"' (1)
starting dose:
0.4 mg PO daily (general prevention); 0.8-1 mg/d in pregnancy; 4 mg/d for women with prior NTD-affected pregnancy; 1 mg/d during methotrexate therapy (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) ·
30 mg PO daily (1/2 grain); titrate by TSH at 6-8 weeks; 60 mg desiccated thyroid is approximately equivalent to 88-100 mcg levothyroxine (1) ·
325 mg PO daily to TID (=65 mg elemental iron/tablet); alternate-day dosing is now favored by hepcidin physiology for better absorption with less GI burden (1) ·
Replacement: 1000 mcg IM daily for 1 week, then weekly for 4 weeks, then monthly; or 1000-2000 mcg PO daily (effective even in pernicious anemia via passive diffusion); intranasal 500 mcg weekly (1)
preparations:
0.4, 0.8, 1 mg OTC; 1 mg Rx; 5 mg/mL injection (1) ·
100, 250, 500, 1000, 5000 mcg tablets (OTC and Rx); 1000 mcg/mL injection; intranasal spray; sublingual (1) ·
15, 30, 60, 90, 120, 180, 240, 300 mg tablets (1/4 to 5 grains; 1 grain = 60 mg) (1) ·
25, 50, 75, 88, 100, 112, 125, 137, 150, 175, 200, 300 mcg tablets; oral capsule and IV/IM also available (1) ·
325 mg tablets (65 mg elemental Fe); 220 mg/5 mL liquid (44 mg elemental Fe/5 mL); 142 mg/mL drops; OTC and Rx (1)
fda max:
routes:
onset:
Hematologic response within days (1) ·
Reticulocyte response at 3-5 days; neurologic recovery weeks to months (and may be incomplete if longstanding) (1) ·
Reticulocyte response at 7-10 days; hemoglobin rise of ~1 g/dL per 3 weeks (1) ·
TSH normalization 4-8 weeks (1) ·
TSH normalization 4-8 weeks; symptomatic improvement weeks to months (1)
duration: (Click arrow to add another value)
halflife:
N/A (incorporated into hemoglobin and tissue stores) (1) ·
T4 ~7 days; T3 ~1 day'"`UNIQ--ref-00000036-QINU`"' (1) ·
~0.5 hours plasma; tissue retention longer (1) ·
~6 days (plasma); hepatic stores last 3-5 years (1) ·
~7 days (euthyroid); longer in hypothyroidism (~9-10 days), shorter in hyperthyroidism'"`UNIQ--ref-00000036-QINU`"' (1)
bioavailability:
10-20% (oral; reduced by food, calcium, antacids, PPIs, tea/coffee; enhanced by ascorbate) (1) ·
40-80% (oral); reduced by food, calcium, iron, PPIs, fiber; take fasting with water'"`UNIQ--ref-00000037-QINU`"' (1) ·
High (oral) (1) ·
Oral ~1-3% via passive diffusion at high doses (independent of intrinsic factor); IM/SC ~100% (1) ·
Variable; reduced by food, calcium, iron, PPIs'"`UNIQ--ref-00000037-QINU`"' (1)
pregnancy:
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.">[[[Pharmacopedia:Citation needed|citation needed]]]</sup> (1) ·
Routinely supplemented in pregnancy and preconception to prevent neural tube defects.<sup class="pcp-cn" title="This claim needs a citation.">[[[Pharmacopedia:Citation needed|citation needed]]]</sup> (1) ·
Routinely supplemented in vegan pregnancies and pernicious anemia.<sup class="pcp-cn" title="This claim needs a citation.">[[[Pharmacopedia:Citation needed|citation needed]]]</sup> (1) ·
Routinely used; iron requirements rise substantially in pregnancy and lactation.<sup class="pcp-cn" title="This claim needs a citation.">[[[Pharmacopedia:Citation needed|citation needed]]]</sup> (1) ·
Synthetic levothyroxine is the standard-of-care in pregnancy; desiccated thyroid use in pregnancy is not well studied<sup class="pcp-cn" title="This claim needs a citation.">[[[Pharmacopedia:Citation needed|citation needed]]]</sup> (1)
Showing below up to 5 results in range #1 to #5.