Pharmaceutical properties

Following oral administration the onset of action is seen after 3-5 days. Levothyroxine as well as liothyronine (= L-triiodothyronine) exhibit an extremely high binding of a specific plasma protein (thyroxine-binding gammaglobuline) of 99.97 % and 99.70, respectively. This protein hormone binding is not covalent and so the bound hormone in plasma is in continuous and very rapid exchange with the fraction of the free hormone. The same applies to exogenous levothyroxine administered during therapy.

Due to its high protein binding thyroid hormones undergo neither hemodialysis nor hemoperfusion.

The bioavailability of levothyroxine sodium as Euthyrox 100 tablets, taken on an empty stomach, was determined to be 79.6 3 %.

The half-life of levothyroxine is on average 7 days. In hyperthyroidism it is shorter (6 days) and in hypothyroidism it is longer (approx. 8 days). The volume of distribution amounts to about 10-12 l. The liver contains 1/3 of the entire extrathyroidal levothyroxine which is rapidly exchangeable with the levothyroxine in serum. Thyroid hormones are metabolized mainly in the liver, kidneys, brain and muscles. The metabolites are excreted with urine and feces. The overall metabolic clearance for levothyroxine is about 1.2 l/day.

Excipients: calcium hydrogen phosphate, corn starch, cellulose, talc, sodium starch glycollate, citric acid, magnesium stearate.

Unknown.

3 years.

Store levothyroxine in a dry place below 25 C.

May 1999