April 1958

Comparative Clinical and Biochemical Effects of the Dextro- and Levo- Isomers of Thyroxine

Author Affiliations

Los Angeles

From the School of Medicine, Department of Medicine, the University of Southern California, and the Thyroid Clinic, Los Angeles County Hospital.

AMA Arch Intern Med. 1958;101(4):722-730. doi:10.1001/archinte.1958.00260160044007

The clinical and physiological comparisons of the isomers of thyroxine by a number of investigators are well summarized by Tabachnik et al. in a recent publication.1 Some excellent animal measurements of oxygen consumption suggest complete lack of potency of the dextro- isomer,2 whereas other studies,3 with use of a different phenomenon, demonstrate physiological activity. Most of these studies were done with racemic mixtures of the two isomers, as compared with the results of the administration of the levo- isomer alone. A generous provision of unlimited quantities of sodium D-thyroxine, suitable for clinical studies, has permitted an extended series of human observations.* Amounts of the sodium D-thyroxine sufficient to administer 100 times the usual levo- isomer dosage have made possible hitherto unavailable comparisons. The present studies, however, were done at the dose levels regularly used clinically in the treatment of hypothyroidism with L-thyroxine.

The chemical characteristics of the

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