The US Food and Drug Administration (FDA) has approved Emcitate (tiratricol), a thyroid hormone receptor agonist, for the treatment of peripheral thyrotoxicosis in adults and paediatric patients with monocarboxylate transporter 8 (MCT8) deficiency, also known as Allan-Herndon-Dudley syndrome.
The approval makes Emcitate the first FDA-approved treatment for MCT8 deficiency in the United States.
Peripheral thyrotoxicosis refers to excess thyroid hormone levels in the bloodstream, which can cause symptoms including rapid heart rate, increased blood pressure and adverse effects on metabolism.
Developed by Swedish pharmaceutical company Egetis Therapeutics, Emcitate is designed to bypass the defective MCT8 transporter and reduce elevated thyroid hormone levels in the blood.
“Until now, patients living with MCT8 deficiency and their families had no FDA-approved treatment option. Emcitate’s approval reflects the FDA’s deep commitment to patients with rare conditions who are in need of meaningful treatment options,” said Marina Zemskova, deputy director of the Division of General Endocrinology in the FDA’s Center for Drug Evaluation and Research.
Egetis Therapeutics CEO Nicklas Westerholm said the company’s immediate focus would be on ensuring that eligible patients can access Emcitate as quickly as possible.
Egetis expects Emcitate to become commercially available in the US within eight to 10 weeks of approval.
How Emcitate works
MCT8 deficiency is a rare, X-linked genetic disorder caused by mutations affecting the SLC16A2 gene, which provides instructions for producing the MCT8 transporter – a critical protein responsible for carrying thyroid hormone into specific cells, including in the brain.
In people with MCT8 deficiency, impaired thyroid hormone transport results in insufficient thyroid hormone availability in the brain while excess thyroid hormone accumulates in the bloodstream. The condition primarily affects males and can cause severe neurodevelopmental and systemic complications.
Patients may experience an inability to walk or sit independently, absent or severely limited speech, intellectual disability, feeding difficulties and chronic cardiovascular and metabolic complications.
“The challenge in treating MCT8 deficiency has always been that the protein needed to deliver thyroid hormone into cells is the one that isn’t working,” said Hylton V. Joffe, director of the Office of Cardiology, Hematology, Endocrinology, and Nephrology in the FDA’s Center for Drug Evaluation and Research.
“This drug sidesteps that problem, as its active ingredient, tiratricol, can enter cells on its own without relying on the broken transporter, leading to a decrease in elevated blood thyroid hormone levels,” he explained.
Clinical studies
The effectiveness of Emcitate was evaluated in two clinical studies involving patients ranging from infants to adults. These included an international, multicentre, randomised, placebo-controlled trial and a longer-term open-label study.
Across the studies, patients treated with Emcitate experienced reductions in excess thyroid hormone levels in the bloodstream, along with improvements in cardiovascular and metabolic symptoms affected by thyroid hormone levels, including systolic blood pressure and heart rate.
Emcitate is administered once daily as tablets for oral suspension, either by mouth or through a feeding tube for patients who have difficulty swallowing.
The most common side effects reported with Emcitate were diarrhoea, vomiting, rash and excessive sweating.
Patients taking another thyroid medication are advised to consult their healthcare provider before starting Emcitate, as the two medicines should not be used together.
Emcitate received Orphan Drug, Rare Pediatric Disease, Fast Track and Breakthrough Therapy designations from the FDA, as well as Priority Review.
In February 2025, the European Commission approved Emcitate as the first treatment for patients with MCT8 deficiency in the European Union.
Emcitate patient support programme
Following the US FDA approval, Egetis has launched Egetis RareLink, a dedicated patient support programme for Emcitate. The programme is intended to help eligible patients access the medicine and provides support for patients, caregivers and healthcare professionals.
As part of its US commercialisation strategy, Egetis has partnered with PANTHERx Rare to support medication access, education, care coordination and ongoing treatment services.
In connection with the Emcitate approval, the FDA also granted Egetis a Rare Pediatric Disease Priority Review Voucher (PRV). The company said it expects to explore monetisation of the voucher, potentially in the fourth quarter of 2026, subject to market conditions.
Egetis has cautioned that Emcitate is not recommended for the treatment of primary hypothyroidism.
