Combined Therapy with L-thyroxine and L-triiodothyronine Compared to L-thyroxine Alone in the Treatment of Primary Hypothyroidism

Objective: The objective of this study was to compare various parameters in patients with hypothyroidism receiving either monotherapy with L-thyroxine (L-T4) or combination therapy with L-T4 and L-triiodothyronine (L-T3).

Design: We conducted a randomized, controlled trial in 36 premenopausal women with hypothyroidism. The patients were divided into two groups: Group A (n=20) received only L-T4, while Group B received the combination L-T4 and L-T3. The treatment period lasted for 6 months.

Results: At baseline, the various parameters examined did not differ in the two groups. No significant difference between monotherapy and combined therapy was demonstrated on TSH level, ECG monitoring, densitometry, or thyroid symptoms score. The lipid profile was better during combined treatment compared to L-T4 alone; in Group A during treatment with L-T4 the levels of cholesterol and low density lipoprotein (LDL) cholesterol were unchanged, while in group B total cholesterol and LDL decreased (p<0.05). The changes in osteocalcin levels did not differ in the two groups, whereas the levels of urine deoxypyridinoline at the end of therapy were higher in the group with combination therapy, compared to monotherapy.

Conclusion: Compared with L-T4 alone, replacement therapy with the combination of L-T4+L-T3 shows favourable changes in serum lipid profile, but higher activation of bone resorption.