This prospective, multicenter open-label study will evaluate the long-term safety, tolerability, PK and PD of AG10 administered on a background of stable heart failure therapy.

An Open-Label Extension and Safety Monitoring Study of Patients with Symptomatic Transthyretin Cardiomyopathy Who Have Completed the Phase II Study AG10-201

The primary objective of this study is to evaluate the long-term safety and tolerability of AG10 administered to adult patients with symptomatic transthyretin amyloid cardiomyopathy (ATTR-CM) in patients who have completed the study AG10-201.

This study will be an Open-Label Extension and Safety Monitoring Study of up to 55 male and/or female patients with symptomatic ATTR-CM aged 18 through 90 years, who have completed the Phase II Study AG10-201. Enrollment into the study will be followed by visits at Day 14, Day 45, 3 Months and every 3 months thereafter until Month 54. After the Month 54 Visit, study visits will be every 6 months. There will be one follow-up visit approximately 30 days after last dose.

If all doses are well tolerated, the duration of each patient's participation in the study will continue based on periodic recommendations of the AG10 Data Monitoring Committee (DMC) and/or registration of the product for the treatment of symptomatic ATTR-CM.

The secondary objectives of this study are to characterize the pharmacokinetics (PK) of AG10 administered orally twice daily in patients with symptomatic ATTR-CM, and to describe the long-term pharmacodynamic (PD) properties of AG10 as assessed by established assays of transthyretin (TTR) stabilization, including Fluorescent Probe Exclusion (FPE) assay and Western blot, and to describe the PK-PD relationship of AG10 in adult patients with symptomatic ATTR-CM.

Inclusion Criteria:

1. Completed participation in study AG10-201.
2. Willing and able to comply with the study medication regimen and all study requirements.
3. The ability to understand and provide informed consent, which must be obtained prior to initiation of study participation.
4. Male patients and female patients of childbearing potential who engage in heterosexual intercourse must agree to use effective method(s) of contraception.

Exclusion Criteria:

1. Hemodynamic instability that would pose too great a risk to the subject.
2. Abnormalities in clinical laboratory tests that would pose too great a risk to the subject.
3. Any clinically significant ongoing medical condition or any laboratory abnormality or condition that could adversely affect the safety of the patient.
4. Known hypersensitivity to study drug (AG10), its metabolites, or formulation excipients.
5. Likely to undergo heart transplantation or placement of a mechanical circulatory device within the next year.
6. Receiving current treatment with diflunisal, tafamidis, green tea, doxycycline, TUDCA/Ursodiol, patisiran, inotersen or any other investigational ATTR agent within 14 days or 5 half-lives of the prior investigational agent (whichever is longer) prior to dosing with study drug.
7. Females who are pregnant or breastfeeding. Lactating females must agree to discontinue nursing before the study drug is administered.