FDA greenlights Emcitate, first treatment for MCT8 deficiency

FDA has approved Emcitate (tiratricol) for the treatment of peripheral thyrotoxicosis in adults and children with monocarboxylate transporter 8 (MCT8) deficiency, also known as Allan-Herndon-Dudley syndrome. It is the first therapy FDA has approved to treat the symptoms of this rare, life-limiting genetic condition.

MCT8 deficiency is caused by mutations in the SLC16A2 gene that impair transport of thyroid hormone into the brain. As a result, patients experience inadequate thyroid hormone activity within the central nervous system alongside excessive circulating triiodothyronine (T3) levels in peripheral tissues, a condition known as peripheral thyrotoxicosis. Many patients experience severe neurodevelopmental impairment, including the inability to walk or sit independently, absent or severely limited speech, intellectual disability, feeding difficulties, and chronic cardiovascular and metabolic stress. The disorder is associated with substantial morbidity and reduced life expectancy.

Emcitate is a thyroid hormone receptor agonist that bypasses the defective transporter underlying the disease. Because tiratricol can enter cells without relying on the MCT8 transporter, it helps reduce elevated thyroid hormone levels.

FDA's decision was supported by clinical studies in patients ranging in age from infants to adults, including the randomized ReTRIACt trial and a longer-term open-label study. Across the studies, treatment reduced excess thyroid hormone levels and improved cardiovascular and metabolic measures associated with thyrotoxicosis, including heart rate and systolic blood pressure.

Emcitate is administered once daily as a liquid suspension and can be given orally or through a feeding tube. The most common adverse reactions were diarrhea, vomiting, rash, and excessive sweating. Clinicians should monitor for signs and symptoms of thyrotoxicosis during treatment initiation and dose titration. Tiratricol may also interfere with T3 laboratory testing, potentially leading to falsely elevated results.

“Until now, patients living with MCT8 deficiency and their families had no FDA-approved treatment option,” said Marina Zemskova, MD, deputy director of the Division of General Endocrinology in FDA's Center for Drug Evaluation and Research. “Emcitate’s approval reflects the FDA’s deep commitment to patients with rare conditions who are in need of meaningful treatment options.”

Sources: FDA. (2026 Sep 28). FDA approves first treatment for MCT8 deficiency; Egetis Therapeutics. (2026 Sep 28). Egetis Therapeutics Announces U.S. FDA Approval of Emcitate (tiratricol) for Patients with MCT8 Deficiency