Summary
Serum 3,3′,5′-triiodothyronine (rT3), 3,5,3′-triiodothyronine (T3), thyroxine (T4) and propylthiouracil (PTU) were measured before and at short intervals for 8 hours after oral administration of 200 mg PTU to six patients with untreated thyrotoxicosis. The study was repeated on the 4th day of treatment with 200 mg PTU every 8 hours. Six other patients with untreated thyrotoxicosis were studied after a single administration of 800 mg PTU.
The results indicated that PTU inhibition of T4 deiodination to T3, evaluated by the fall in serum T3, was of the same duration as the PTU inhibition of rT3 deiodination, evaluated by the increase in serum rT3. After 200 mg PTU inhibition was maximal for only a few hours, and there was no cumulative effect of PTU during the first four days of treatment, when 200 mg PTU was given every 8 hours. After 800 mg PTU the full effect was maintained for the 9 hour period studied, after which serum T3 had fallen to 65 ± 2 % of the pretreatment level (mean ± SE). Thus, to obtain a permanent full effect of PTU on iodothyronine deiodination during the treatment of thyrotoxicosis it is necessary to use large doses or frequent administration.
Key-Words:
Thyrotoxicosis
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Propylthiouracil
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T
4 Deiodination
