Aims: The prevalence of intolerance to lactose-containing foods is present at birth in humans and gradually declines with age. In hypothyroid patients requiring high doses of levothyroxine (L-T4) to achieve euthyroidism, lactose intolerance (LI) should be excluded due to its high prevalence in the general population. The absorption of oral T4 may be affected in patients with LI, by following a diet containing lactose, while it improves with a lactose-free diet. Lactose is often present in many commercially available drugs, as L-T4 preparations. We aimed at investigating patients with LI and hypothyroidism, who were initially treated with “L-T4 in tablet form containing lactose” (L-T4-Tab+Lactose), and then switched to the same dose of “liquid L-T4 oral solution (lactose-free)” (L-T4-Liq).
Methods: We have enrolled 20 patients treated with L-T4-Tab+Lactose, with stable TSH value in the normal range in the last 2 years. Because of a new diagnosis of LI, patients were switched from L-T4-Tab+Lactose to L-T4-Liq. All patients were diagnosed to be affected by LI, and were taking a low lactose diet. L-T4 was then supplied again at the same dosage in tablets in 8 patients who wished to switch back to the tablet form.
Results: The L-T4-Liq formulation showed a better control of TSH levels, all patients (included those who had been switched back to tablets) were lastly treated with the L-T4-Liq, and TSH, FT3, FT4 were tested again two months after the initial evaluation, and after 12, and 24 months, resulting in the normal range in all subjects.
Conclusion: The L-T4-Liq formulation is able to bypass the issue of LI malabsorption, and can lead to the normalization of TSH, and long term stable TSH levels, in patients with subclinical hypothyroidism. Additional researches are necessary to evaluate the liquid L-T4 formulation in larger numbers of patients with hypothyroidism and lactose intolerance.