Safety, Tolerability, and Efficacy of Encaleret in Participants With Autosomal Dominant Hypocalcemia (ADH) Type 1

A Phase 2b, Open-label Dose-ranging Study Evaluating the Safety, Tolerability, Pharmacodynamics and Pharmacokinetics, and Efficacy of CLTX-305 (Encaleret) in Autosomal Dominant Hypocalcemia (ADH) Type 1

The primary purpose of this study is to evaluate the safety, tolerability and effectiveness of encaleret in participants with Autosomal Dominant Hypocalcemia Type 1 (ADH1).

Key Inclusion Criteria:

• Be able to understand and sign a written informed consent or assent form, which must be obtained prior to initiation of study procedures.
• Postmenopausal women are allowed to participate in this study
• Body mass index (BMI) ≥ 18.5 to < 39 kilograms (kg)/square meter (m^2)
• Have an activating mutation of the Calcium-sensing receptor (CASR) gene
• Participants being treated with thiazide diuretics may be enrolled if they are willing and able to discontinue thiazides
• Participants being treated with strong Cytochrome P3A4 (CYP3A4) inhibitors should ideally, if clinically appropriate, discontinue these medications during the screening period
• Participants being treated with magnesium or potassium citrate supplements should discontinue such treatment starting on Day -1 during Period 1 and Period 2 and may be asked to discontinue treatment during Period 3

Key Exclusion Criteria:

• History of treatment with parathyroid hormone (PTH) 1-84 or 1-34 within the previous 3 months
• History of hypocalcemic seizure within the past 3 months
• Blood 25-OH Vitamin D level < 25 nanograms (ng)/milliliter (mL)
• Participants with hemoglobin (Hgb) < 13 grams (g)/deciliter (dL) for men and < 12 g/dL for women
• Estimated glomerular filtration rate (eGFR) < 25 mL/minute/1.73 m^2 using Chronic Kidney Disease Epidemiology Collaboration (for participants <18 years old the Schwartz equation will be calculated)
• 12-lead resting electrocardiogram (ECG) with clinically significant abnormalities
• Participants with positive hepatitis B surface antigen (HBsAg), hepatitis A immunoglobulin M (IgM), or human immunodeficiency virus (HIV) viral serology test results at the Screening Visit
• Pregnant or nursing (lactating) women
• History of drug or alcohol dependency within 12 months preceding the Screening Visit
• History of thyroid or parathyroid surgery
• Current participation in other investigational drug studies
• Unwillingness to refrain from blood donation within 12 weeks prior to Screening Visit from the start of the study enrollment through one year after the last dose of the study drug

Note: Other protocol defined Inclusion/Exclusion criteria may apply.