Bioequivalence and Bioavailability Forum

Dear members,

It is a challenge to determine the bioavailability of levothyroxine sodium products because levothyroxine is naturally present in minute quantities in the blood, with the total levels reaching 5.0-12.0 mg/dl and free (or unbound) levels reaching 0.8-2.7 ng/dl in a healthy adult. To assess the bioavailability of levothyroxine sodium after a single dose, several times the normal dose should be given to raise the levels of the drug significantly above baseline to allow measurement.

This is the statement from USFDA recommendations. Considering the endogenous levels present in the body it is difficult to validate the method using normal plasma/serum

Will FDA accept validation using other type of plasma, i.e. charcoal treated plasma or Bovine serum

Alternatively if anyone has experience with this molecule, request you to share your thoughts

Regards
Chirag