[The effect of three kinds of thyroid hormone preparations on serum thyroid hormone and TSH in primary hypothyroidism].Zhongguo Yi Xue Ke Xue Yuan Xue Bao. 1990 Dec; 12(6):421-4.ZY
Thirty-eight cases of primary hypothyroidism were treated prospectively with three kinds of thyroid hormone preparations, including Levothyroxine, L-triiodothyronine and dry thyroid preparation. A protocol of different dosages with same biologic effects was followed: 100 micrograms Levothyroxine approximately 40-60 mg dry thyroid preparation approximately 30-40 micrograms L-triiodothyronine. During drug replacement treatment, the change serum T3 and TSH is more sensitive than that of serum T4 and reverse T3. Both of serum T3 and T4 can directly inhibit the secretion of pituitary TSH, but serum T4 is more closely related to TSH than is T3. In judging the overdose, the level of serum T4 is a superior indicator to the level of T3. The best time to take thyroid hormone preparations is at bedtime.