FDA Approves Emcitate as First Treatment for Peripheral Thyrotoxicosis in MCT8 Deficiency

The FDA has approved tiratricol (Emcitate, Egetis Therapeutics) tablets for oral suspension to treat peripheral thyrotoxicosis in adults and pediatric patients with monocarboxylate transporter 8 (MCT8) deficiency, also known as Allan-Herndon-Dudley syndrome. The agency said it is the first FDA-approved therapy to treat symptoms of the disease.

MCT8 deficiency is a rare, X-linked disorder caused by pathogenic mutations in the SLC16A2 gene, Egetis reported. Without a functioning MCT8 transporter, thyroid hormone cannot cross the blood-brain barrier, so the brain receives too little hormone while excess levels build up in the bloodstream, the FDA said. Tiratricol, a thyroid hormone receptor agonist, can enter cells without relying on the transporter, the agency said.

Efficacy was evaluated in 2 clinical studies in patients ranging from infants to adults: an international, multicenter, randomized, placebo-controlled trial (NCT02060474) and a longer-term open-label study (Triac Trial II). Across both studies, treated patients had reductions in excess blood thyroid hormone levels and improvements in cardiovascular and metabolic symptoms, such as systolic blood pressure and heart rate, the FDA reported.

The label includes a boxed warning against use for obesity or weight loss, and primary hyperthyroidism is a contraindication. Warnings include thyrotoxicosis during treatment initiation and dose titration, and tiratricol can cross-react with T3 immunoassays, causing T3 overestimation. According to the FDA, tiratricol should not be used together with another thyroid medication. The most common adverse reactions (≥5%) were diarrhea, vomiting, rash, and hyperhidrosis. Tiratricol is not recommended for treatment of primary hypothyroidism.

Tiratricol is taken once daily as a liquid suspension by mouth or feeding tube. The drug received Orphan Drug, Rare Pediatric Disease, Fast Track, and Breakthrough Therapy designations and Priority Review, and Egetis was granted a Rare Pediatric Disease priority review voucher. The company expects US commercial availability 8 to 10 weeks after approval.

Sources: US Food and Drug Administration. FDA approves first treatment for MCT8 deficiency. Press release. US Food and Drug Administration; September 28, 2026. Accessed September 29, 2026.

Egetis Therapeutics. Egetis Therapeutics announces US FDA approval of EMCITATE (tiratricol) for patients with MCT8 deficiency. Press release. Egetis Therapeutics; September 28, 2026. Accessed September 29, 2026.