Drilldown: Medicines

Fexofenadine (1) · Levothyroxine (1) · Thyroid (desiccated) (1)

Allegra, Allegra Allergy 24 Hour, Mucinex Allergy (combo) — all now OTC in US (1) · Armour Thyroid, NP Thyroid, Nature-Throid, WP Thyroid (1) · Synthroid, Levoxyl, Tirosint, Unithroid, Euthyrox (1)

[[:Category:Antihistamines|Antihistamine]] (1) · [[:Category:H1_receptor_antagonists|Histamine H1 receptor antagonist (second-generation)]] (1) · [[:Category:Hormone_replacement|Hormone replacement]] (2) · [[:Category:Thyroid_hormones|Thyroid hormone]] (2)

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-00000016-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-00000017-QINU`"'. (1) · '"`UNIQ--vote-00000CC9-QINU`"' Mostly excreted unchanged in feces and urine; P-glycoprotein substrate (the basis of the fruit-juice interaction). (1)

'"`UNIQ--vote-00000018-QINU`"', '"`UNIQ--vote-00000019-QINU`"' (1) · '"`UNIQ--vote-00000033-QINU`"', '"`UNIQ--vote-00000034-QINU`"', '"`UNIQ--vote-00000035-QINU`"' (1) · '"`UNIQ--vote-00000CCA-QINU`"', '"`UNIQ--vote-00000CCB-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) · 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) · 60 mg PO BID or 180 mg PO once daily (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) · 30, 60, 180 mg tablets; 30 mg ODT; 6 mg/mL oral suspension; all OTC (1)

None · Indication-specific · 40 mg/d · 10 mg/d · 20 mg/d · 80 mg/d · 10 mg/d (adults) · 100 mg/d · 4 g/d · 400 mg/d · 40 mg/d typical; up to 240 mg/d for Zollinger-Ellison · 5 mg/d · 50 mg/d · 600 mg/d · No fixed ceiling; titrate to clinical effect and tolerability with CDC opioid prescribing guidance constraints on morphine-milligram-equivalent (MME) totals · No fixed maximum; titrated to TSH target · TID per eye · Titrated to glucose; no fixed ceiling · Titrated to glucose; no fixed maximum · '''20 mg/day in adults >60 years''' per FDA's 2011-2012 QT-prolongation warning; 40 mg/day in adults ≤60

Other values:

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IV (1) · Oral (3)

1-2 hours (1) · TSH normalization 4-8 weeks (1) · TSH normalization 4-8 weeks; symptomatic improvement weeks to months (1)

12-24 hours (1) · Steady-state at 4-6 weeks (2)

T4 ~7 days; T3 ~1 day'"`UNIQ--ref-0000001A-QINU`"' (1) · ~14 hours'"`UNIQ--ref-00000CCC-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) · Variable; reduced by food, calcium, iron, PPIs'"`UNIQ--ref-0000001B-QINU`"' (1) · ~33% (oral; fruit juices including grapefruit, orange, and apple reduce absorption substantially via OATP1A2 inhibition — distinctive interaction not seen with most other H1s)'"`UNIQ--ref-00000CCD-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) · Generally considered safe; loratadine and cetirizine have more pregnancy data and are typically preferred.<sup class="pcp-cn" title="This claim needs a citation.">&#91;[[Pharmacopedia:Citation needed|citation&nbsp;needed]]&#93;</sup> (1) · Synthetic levothyroxine is the standard-of-care in pregnancy; desiccated thyroid use in pregnancy is not well studied.'"`UNIQ--ref-0000001C-QINU`"' (1)

OTC in US (1) · [[USLegal:Prescription only|Rx-only]] in US (2)