Peripheral markers of thyroid function: the effect of T4 monotherapy vs T4/T3 combination therapy in hypothyroid subjects in a randomized crossover study.

Background: A recent randomized controlled trial suggests that hypothyroid subjects may find levothyroxine (l-T4) and levotriiodothyronine combination therapy to be superior to l-T4 monotherapy in terms of quality of life, suggesting that the brain registered increased T3 availability during the combination therapy.

Hypothesis: Peripheral tissue might also be stimulated during T4/T3 combination therapy compared with T4 monotherapy.

Methods: Serum levels of sex hormone-binding globulin (SHBG), pro-collagen-1-N-terminal peptide (PINP), and N-terminal pro-brain natriuretic peptide (NT-proBNP) (representing hepatocyte, osteoblast, and cardiomyocyte stimulation respectively) were measured in 26 hypothyroid subjects in a double-blind, randomized, crossover trial, which compared the replacement therapy with T4/T3 in combination (50 μg T4 was substituted with 20 μg T3) to T4 alone (once daily regimens).

Effect of combination therapy with thyroxine (T4) and 3,5,3'-triiodothyronine versus T4 monotherapy in patients with hypothyroidism, a double-blind, randomised cross-over study.

Background: Treatment of hypothyroidism with 3,5,3'-triiodothyronine (T(3)) is controversial. A recent meta-analysis concludes that no evidence is present in favour of using T(3). However, the analysis included a mixture of different patient groups and dose-regimens.