Table 2.

FDA therapeutic equivalence ratings for currently available levothyroxine tablet products [25–33]

Levothyroxine tablet product	Reference listed druga	Therapeutic equivalence codeb	Inactive ingredientsc
Brand name
Unithroid	Yes	AB1, AB2, AB3	Acacia, colloidal silicon dioxide, corn starch, lactose, magnesium stearate, microcrystalline cellulose, sodium starch glycolate
Synthroid	Yes	AB1, AB2	Acacia, confectioner’s sugar (contains corn starch), lactose monohydrate, magnesium stearate, povidone, talc
Levoxyl	Yes	AB1, AB3	Calcium sulfate dehydrate, croscarmellose sodium, magnesium stearate, microcrystalline cellulose, sodium bicarbonate
Levo-T	No	AB1, AB2, AB3	Magnesium stearate, microcrystalline cellulose, colloidal silicone dioxide, sodium starch glycolate
Euthyrox	No	AB2	Citric acid anhydrous, corn starch, gelatin, magnesium stearate, mannitol, sodium croscarmellose
Generic
Levothyroxine sodium (Mylan)	No	AB1, AB2, AB3, AB4	Butylated hydroxyanisole, colloidal silicon dioxide, crospovidone, ethyl alcohol, magnesium stearate, mannitol, microcrystalline cellulose, povidone, sodium lauryl sulfate, sucrose

^aA drug identified by the FDA as a product on which an applicant relies in seeking approval of an abbreviated new drug application for a generic product

^bIf bioequivalence to a reference listed drug product is demonstrated, the product will be given the same code as the reference listed drug it was compared against: AB1 vs. Unithroid, AB2 vs. Synthroid, AB3 vs. Levoxyl; AB4 vs. Levothroid/Thyro-Tabs (now discontinued). One common code indicates therapeutic equivalence between products

^cAll formulations except Euthyrox also contain colorants that differ according to tablet dose