Phase 2 Study of the PTH-Independent Effects of Encaleret on Mineral Homeostasis in Subjects With Post-Surgical Hypoparathyroidism (PSH)
Background: Parathyroid glands in the neck make a hormone that keeps blood calcium levels stable. Sometimes these glands are damaged or removed during neck surgery. This can lead to a condition called postsurgical hypoparathyroidism (PSH). People with PSH have low levels of calcium in their blood. Calcium and vitamin D pills can help them keep their blood calcium levels steady. But this can increase calcium in the urine and result in kidney problems. New treatments for PSH are needed.
Objective: To test a drug (encaleret) in people with PSH.
Eligibility: People aged 18 or older who have PSH.
Design: Participants will be in the study for 6 months. They will have a screening visit and a treatment visit. Screening will take up to 2 days. Participants will have a physical exam. They will have blood and urine tests and tests of their heart function. They will have an ultrasound of their kidneys; they will lie on a table for 15 to 30 minutes while a wand is moved over their back. Treatment will require participants to stay in the clinic for 7 days and 6 nights. They will take the study drug (encaleret) by mouth twice a day for 5 days. They will have a small, flexible tube inserted into a vein; this will remain in place during the visit. Blood samples will be taken through the tube 4 to 9 times each day. Participants urine will be collected. Participants will have follow-up blood tests 1 week after leaving the clinic. They will have 3 follow-up phone calls.
‣ Participants must meet the following criteria for inclusion during screening:
• Be able to understand and sign a written informed consent form, which must be obtained prior to initiation of study procedures.
• Age \>= 18 years
• Postmenopausal women are allowed to participate in this study:
• a. Women are considered postmenopausal and not of childbearing potential if they have had 12 months of natural (spontaneous) amenorrhea with an appropriate clinical profile (e.g., age appropriate, history of vasomotor symptoms) or have had surgical bilateral oophorectomy (with or without hysterectomy) or tubal ligation at least 6 weeks prior to start of the study. In the case of oophorectomy alone, only when the reproductive status of the woman has been confirmed by follow up hormone level assessment, shall she be considered not of childbearing potential.
• Body mass index (BMI) \>= 18.5 to \< 39 kg/m\^2
• Have a diagnosis of PSH, either permanent PSH (Cohort 1, surgery \>= 12 months ago) or recent PSH (Cohort 2, surgery \< 12 months ago).
• Participants must have achieved an albumin-corrected blood calcium level of 7.8-10.2 mg/dL on conventional therapy without significant symptoms of hypocalcemia or hypercalcemia.
• Participants being treated with thiazide diuretics may be enrolled if they are willing and able to discontinue thiazides for at least 5 half-lives prior to initiation of encaleret and remain off during the study treatment period. (5 half-lives of hydrochlorothiazide = 75 hours; chlorothiazide = 10 hours; chlorthalidone = 12.5 days). If the thiazide is being used as an antihypertensive, as opposed to use as a urine calcium-lowering drug, alternative therapy will be offered.
• Participants being treated with strong CYP3A4 inhibitors (including clarithromycin, telithromycin, nefazodone, itraconazole, ketoconazole, atazanavir, darunavir, indinavir, lopinavir, nelfinavir, ritonavir, saquinavir, tipranavir) may be enrolled if they are willing and able to discontinue these medications for at least 5 half-lives prior to initiation of encaleret and remain off during the study treatment period.
• Participants being treated with magnesium or potassium citrate supplements should discontinue such treatment starting on Day -2.
⁃ Participants being treated with medications that have impacts on mineral metabolism which investigators believe may impact study endpoints may be enrolled if they are willing and safely able to discontinue the medication for at least 5 half-lives prior to initiation of encaleret and remain off during the study treatment period