Table 1: Summary of Levothyroxine PK.

Pharmacokinetic Characteristic	Description
Main site of absorption	Small intestine (jejunum and ileum)
Bioavailability	70–80 % in euthyroid person; may be slightly higher in hyperthyroid patients
Tmax	2–3 hours
Vd	11–15 L
Protein binding	T4 >99.9 % T3 = 99.8 %
T1/2	T4 = 6.2 and 7.5 days in euthyroid and hypothyroid patients, respectively T3 = 1.0 and 1.4 days in euthyroid and hypothyroid patients, respectively
CL	T4 = 0.055 and 0.038 L/h in euthyroid and hypothyroid patients, respectively

Vd = Volume of distribution; L = Litres; CL = Clearance