General Description
Dextrothyroxine sodium,O-(4-hydroxy-3,5-diiodophenyl)-3,5-diiodo-D-tyrosinemonosodium salt hydrate, sodium D-3,3 ,5,5 -tetraiodothyronine(Choloxin), occurs as a light yellow to buffpowder. It is stable in dry air but discolors on exposure tolight; hence, it should be stored in light-resistant containers.It is very slightly soluble in water, slightly soluble in alcohol,and insoluble in acetone, chloroform, and ether.The hormones secreted by the thyroid gland have markedhypocholesterolemic activity along with their other wellknownactions. The finding that not all active thyroid principlespossessed the same degree of physiological actionsled to a search for congeners that would cause a decrease inserum cholesterol levels without other effects such as anginapectoris, palpitation, and congestive failure. D-Thyroxineresulted from this search. At the dosage required, however,L-thyroxine contamination must be minimal; otherwise, itwill exert its characteristic actions. One route to opticallypure (at least 99% pure) D-thyroxine is the use of an L-aminoacid oxidase from snake venom, which acts only on theL-isomer and makes separation possible.
Clinical Use
D-Thyroxine monosodium salt potentiates the action of anticoagulants suchas warfarin or dicumarol; thus, the dosage of the anticoagulantsused concurrently should be reduced by one third andthen, if necessary, further modified to maintain the prothrombintime within the desired limits.
