Levothyroxine

Synthroid, Levoxyl, Tirosint

Thyroid hormone • Synthetic T4

NTI

Half-life

6-7 days

Protein Binding

>99%

Metabolized By

N/A

External

Synthetic thyroxine (T4) that is converted to active T3, regulating metabolism

Drug Class

Thyroid hormone

Subclass

Synthetic T4

SynthroidLevoxylTirosint

Half-life

6-7 days

Time for plasma concentration to decrease by 50%

Protein Binding

>99%

Fraction bound to plasma proteins

Therapeutic Index

Narrow

Margin between therapeutic and toxic doses

•Should not be used for weight loss — doses within or above normal range are ineffective and potentially toxic