Emcitate

MCT8 deficiency causes cerebral hypothyroidism and peripheral thyrotoxicosis. In an international natural-history cohort of 151 participants, 32 (21%) died; estimated median overall survival was 35.0 years, with a 95% confidence interval of 8.3 to 61.7 years. In a caregiver survey, 54.5% of affected individuals had no head control and none could sit or walk without support. A U.S. healthcare-cost study analyzed 44 individuals with confirmed MCT8 deficiency and reported all-cause costs of $245,393 per patient per year.

The FDA approved tiratricol on 28 September 2026 on the basis of two studies. In Study 1 (NCT05579327, ReTRIACt), 15 participants on a stable dose were randomized to placebo (8) or continued tiratricol (7) for 30 days; the ratio of the serum total T3 rate of change (placebo/tiratricol) was 1.5 (95% CI 1.0 to 2.2; p=0.034), and the rescue criterion was met by 4 of 8 placebo participants (50.0%) and 1 of 7 tiratricol participants (14.3%, one premature discontinuation counted as rescue), a difference in proportions of 0.36 (95% CI -0.16 to 0.77). In Study 2 (NCT02060474, Triac Trial I), 46 participants were enrolled; among 45 analyzed, mean serum total T3 decreased by 205.2 ng/dL (95% CI 174.6 to 235.7) from a baseline of 323.4 ng/dL at month 12, with mean changes of -8.9 beats per minute in heart rate (34 participants) and -4.1 mmHg in systolic blood pressure (35 participants). Triac Trial II enrolled 22 participants younger than 30 months and did not meet its co-primary neurodevelopmental endpoints, although serum T3 concentrations decreased. The most common adverse reactions in the prescribing information are diarrhea, vomiting, rash, and hyperhidrosis, each reported in 0% to 13% of participants per study, and the label carries a boxed warning against use for the treatment of obesity or for weight loss.

Tiratricol is the first FDA-approved treatment for MCT8 deficiency. The U.S. indication, approved on 28 September 2026, is peripheral thyrotoxicosis in adults and pediatric patients with MCT8 deficiency, and the label states that tiratricol is not recommended for primary hypothyroidism; the EU indication, authorised in February 2025, is peripheral thyrotoxicosis in MCT8 deficiency from birth. The efficacy evidence in the label consists of serum total T3 lowering in a 30-day randomized withdrawal study of 15 participants and a 12-month single-arm study of 46 participants, with secondary changes in heart rate, systolic blood pressure, and body weight. Triac Trial II did not meet its co-primary neurodevelopmental endpoints. Dosing is titrated to total T3 measured by LC-MS/MS, and the label states that no FDA-authorized LC-MS/MS test for total T3 is currently available. Egetis expects U.S. commercial availability eight to ten weeks after approval, with dispensing through PANTHERx Rare.