Levothyroxine (Synthroid, Levoxyl, Levothroid, Unithroid) -- In active form, influences growth and maturation of tissues. Involved in normal growth, metabolism, and development. Produces stable levels of T3 and T4. Administered as a single dose in the morning on an empty stomach. May be administered PO/IV/IM. Has long half-life (7-10 d), and parenteral dosing is rarely needed (except when PO is unavailable, patient is on continuous enteral feeds, or in emergency, such as myxedema coma). Initial subtherapeutic doses are recommended to avoid the stress of rapid metabolic change in elderly patients and in those with coronary artery disease or severe COPD.