Elsevier

Metabolism

Volume 27, Issue 10, October 1978, Pages 1518-1525
Metabolism

A comparison of thyroxine and desiccated thyroid in patients with primary hypothyroidism*

https://doi.org/10.1016/S0026-0495(78)80024-9Get rights and content

Patients with primary hypothroidism were treated with graded increments of thyroxine (T4) and/or desiccated thyroid; the thyrotropin (TSH) response to thyrotropin releasing hormone (TRH) was studied after each increment. The biologic effect of the two therapies was compared by estimating by interpolation the dose of thyroid hormone that caused the peak serum TSH after TRH to fall to 5 μU/ml. In 12 patients, the average dose of T4 required to reach this end-point was 176 μg/day. In nine patients, the average dose of desiccated thyroid required was 138 mg/day. The range of the required dose in the patients studied was about twofold (T4: 100–245 μg/day; desiccated thyroid: 114–180 mg/day).

Based on those patients who received both therapies (n=6), the mean relative potency of T4 to desiccated thyroid was 0.99×103. Thus, a daily dose of 100 μg of T4 was on average equal in biologic activity to 101 mg of desiccated thyroid; 60 mg of desiccated thyroid was equal to 60 μg of T4. However, among individual patients, there was a 1.6-fold range in the relative potency of T4 to desiccated thyroid (0.81×103−1.29×103).

In five patients, while the dose of thyroid hormone was being increased, the TSH response to TRH increased before it fell; thus TSH secretion can be relatively sluggish in more severe hypothyroidism (pituitary myxedema).

These data define the relative biologic effect in man of the two most commonly used forms of thyroid therapy and should be of use when consiering or evaluating a change in therapy for patients with primary hypothyroidism.

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    *

    Supported by the Medical Research Service of the Veterans Administration and by USPHS Grant no. HD-7181.

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