Liothyronine sodium tablets

The synthetic preparations used are the sodium salts of the natural isomers of the thyroid hormones. Levothyroxine sodium (L-T, synthroid, levoxyl, levothroid, unithroid, others) is available in tablets in a variety of doses and as a lyophilized powder for injection. L-T has a narrow therapeutic index, and the FDA has mandated demonstration of bioequivalence for brand and generic preparations by the various producers. Liothyronine sodium (L-Tft is available in tablets (cytomel) and in an injectable form (triostat). A mixture of L-T and L-T is marketed as liotrix (thyroiar). Desiccated thyroid preparations, derived from whole animal thyroids and containing both T and T have highly variable biologic activity and are much less desirable. 

Rapaka, R.S. Knight, P.W. Prasad, V.K. Reversed-phase high-performance liquid chromatographic analysis of liothyronine sodium and levothyroxine sodium in tablet formulations preliminary studies on dissolution and content uniformity. J.Pharm.Sci., 1981, 70, 131-134... 

Tablets of Liothyronine Sodium, B.P. May be of any strength between 5 and 50 micrograms. These tablets contain too much organic matter in relation to iodine content for application of the flask-combustion method.

Despite the fact that a biological method is the only way to obtain a reliable estimate of the potency of thyroid, chemical assessment is still quite frequently required. The B.P, method is a determination of so-called iodine in combination as thyroxine and is based on the observations of Harington and Randall that, after hydrolysis of the thyroid with sodium hydroxide, an acid-insoluble fraction can be separated which consists essentially of thyroxine. There have always been mechanical difficulties associated with this assay, especially when an attempt is made to apply it to formulated products such as tablets. Further considerations, however, indicate that it is an unreliable guide to the potency of thyroid. Firstly, the discovery of the highly potent 3,5,3 -tri-iodothyronine (liothyronine) invalidates the assumption that the amount of total iodine in the acid-insoluble fraction is related to the proportion of thyroxine and hence to potency secondly it has been shown that when lactose is present during the hydrolysis stage a greater proportion of iodine is present in the subsequent acid-precipitated fraction than if the lactose is absent. This observation was first made by Doery and has since been confirmed in a... 

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