12
Treatment
Table 1. Thyroid Hormone Preparations
Thyroid Hormone
Products
Available Oral Forms Doses
Levothyroxine
Levo-T
®
,
Levothroid
®
,
Levoxyl
®
,
Synthroid
®
,
Unithroid
®
,
generic
Tablets 25-300 mcg
Tirosint
®
Gelatin capsules 13-150 mcg
Liothyronine
Cytomel
®
,
generic
Tablets 5, 25, 50 mcg
yroid extract
Armour yroid
®
,
Nature roid
®
,
NP yroid
Tablets 15-325 mg
Table 2. Medications Potentially Affecting Levothyroxine
Dose Requirement
Examples of Drugs
Potential
Mechanism
Possible Effect
on Serum TSH
Potential
Effect on
LT4 dose
requirement
Calcium carbonate,
proton pump inhibitors,
cholestyramine, colesevelam,
selevamer, ferrous sulfate,
aluminum-containing antacids,
sucralfate, raloxifene, orlistat,
multivitamins containing
calcium and ferrous sulfate
Decreased LT4
absorption
Increased
TSH
Increased
dose
Estrogen, tamoxifen, raloxifene,
clofibrate, opioids, mitotane,
fluorouracil, capecitabine
Increased LT4
transport by
thyroxine-
binding globulin
Increased
TSH
Increased
dose
Androgens, anabolic steroids Decreased
LT4 transport
by thyroxine-
binding globulin
Decreased
TSH
Decreased
dose
Phenobarbital, phenytoin,
carbamazepine, rifampin,
sertraline, imatinib
Increased
hepatic
metabolism
Increased
TSH
Increased
dose
Tyrosine kinase inhibitors (e.g.
imatinib, motesanib, sorafenib,
sunitinib, and vandetanib)
Increased
conversion of
T3 to reverse T3
Increased
TSH
Increased
dose
