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Protocol Details

A Phase IIb, Open-label Dose-ranging Study Evaluating the Safety, Tolerability, Pharmacodynamics and Pharmacokinetics, and Efficacy of CLTX-305 (encaleret) in Autosomal Dominant Hypocalcemia Type 1 (ADH1)

This study is NOT currently recruiting participants.

Summary | Eligibility | Citations | Contacts




Sponsoring Institute

National Institute of Dental And Craniofacial Research (NIDCR)

Recruitment Detail

Type: Completed Study; data analyses ongoing
Gender: Male & Female
Min Age: 16 Years
Max Age: 100 Years

Referral Letter Required


Population Exclusion(s)

Pregnant Women



Recruitment Keyword(s)




Investigational Drug(s)

CLTX-305 (encaleret)

Investigational Device(s)



Drug: CLTX-305 (encaleret)

Supporting Site

National Institute of Dental and Craniofacial Research


The Calcium-Sensing Receptor (CaSR) detects the amount of calcium in the blood and urine. Parathyroid hormone (PTH) helps keep blood calcium levels normal. When PTH and calcium blood levels are low, this is called hypoparathyroidism. People with changes in the CaSR have a type of hypoparathyroidism called ADH1. ADH1 is treated with calcium supplements and vitamin D. But these do not always work, and can cause problems like kidney stones. Researchers want to see if the drug CLTX-305 is a better treatment option.


To see if CLTX-305 is safe and works in people with ADH1.


People ages 16 and older with ADH1


Participants will be screened with:

Medical history

Physical exam

Kidney ultrasound: Participants will lie on a table while a wand is moved over their back.

Bone density test: Participants will lie on a table while an X-ray machine moves around them.

Blood, urine, and heart tests

The study is split into 3 periods. Participants may take part in some or all periods.

In Periods 1 and 2, participants will take CLTX-305 by mouth once or twice daily for up to 5 days. Participants will stay at the NIH for 7 days and 6 nights.

In Period 3, participants will take CLTX-305 at home for 24 weeks. They will have 3 inpatient visits that last 1 2 days each.

Screening tests will be repeated during the study. Blood and urine will be collected often.

Participants dose of calcium and vitamin D may be changed. They may be asked to stop taking other medicines or change the dose.

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Participants must meet the following criteria for inclusion during screening:

-Be able to understand and sign a written informed consent or assent form, which must be obtained prior to initiation of study procedures.

-Age >= 16 years

-Postmenopausal women are allowed to participate in this study:

--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/m2

-Have an activating mutation of the CaSR gene

-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 CLTX-305 (encaleret) and during the study treatment period. When the thiazide is being used as an antihypertensive, 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) should ideally, if clinically appropriate, discontinue these medications during the screening period for at least 5 half-lives prior to initiation of CLTX-305 (encaleret). Participants who must remain on strong CYP3A4 inhibitors may still enroll if they are able to remain on their medications at stable doses throughout the trial.

-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 if the blood magnesium and urine citrate are within the normal ranges during Period 1 and Period 2.


Participants who meet any of the following criteria during Screening will not be eligible to participate in the study:

-History of treatment with 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 ng/mL

--If participant has a blood 25-OH Vitamin D level < 25 ng/mL at the screening visit, they will be prescribed cholecalciferol or ergocalciferol supplementation. Once the 25-OH Vitamin D level is > 25 ng/mL, the participant will be eligible to continue to the treatment phase of the study.

-Participants with hemoglobin (Hgb) < 13 g/dL for men and < 12 g/dL for women

--If participant has a low Hgb at the screening visit due to iron, B12, or folate deficiency, they will be prescribed supplementation. Once the Hgb level is > 13 in men or > 12 in women, the participants will be eligible to continue to the treatment phase of the study.

-Abnormal laboratory values which in the opinion of the investigator, would make the participant not suitable for participation in the study

-Estimated glomerular filtration rate (eGFR) < 25 mL/minute/1.73 m2 using CKD-EPI (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. Participants who are in complete remission from Hepatitis C as evidence by sensitive assay >=12 weeks after completion of HCV therapy are allowed to participate in the study.

-Pregnant or nursing (lactating) women, where pregnancy is defined as the state of a female after conception and until the termination of gestation, confirmed by a positive serum hCG laboratory test

-Women of child-bearing potential, defined as all women physiologically capable of becoming pregnant, unless they are using highly effective methods of contraception during dosing and for 3 months following the discontinuation of study treatment. Highly effective contraception methods include:

--Total abstinence (when this is in line with the preferred and usual lifestyle of the participant). Periodic abstinence (e.g., calendar, ovulation, symptothermal, postovulation methods) and withdrawal are not acceptable methods of contraception.

--Female sterilization (have had surgical bilateral oophorectomy with or without hysterectomy) or tubal ligation at least six weeks before taking study treatment. In case of oophorectomy alone, only when the reproductive status of the woman has been confirmed by follow up hormone level assessment.

--Male sterilization (at least 6 months prior to screening). For female participants on the study the vasectomized male partner should be the sole partner for that participant.

-Combination of the following (a+b or a+c, or b+c):

--Use of oral, injected or implanted hormonal methods of contraception or other forms of hormonal contraception that have comparable efficacy (failure rate <1%), for example hormone vaginal ring or transdermal hormone contraception

--Placement of an intrauterine device (IUD) or intrauterine system (IUS)

--Barrier methods of contraception: Condom or Occlusive cap (diaphragm or cervical/vault caps) with spermicidal foam/gel/film/cream/vaginal suppository

-Sexually active male participants who are unwilling to use a condom during vaginal intercourse while taking the CLTX-305 (encaleret) (study drug) and for 3 months after the last dose of the study drug. Participants should not father a child during active participation in the study starting with the first CLTX-305 (encaleret) dose in Period 1, Period 2 (for Cohort 2) until the end of study participation. Condoms are not required if the participant is vasectomized or if the participant s partner is not a woman of childbearing potential.

-Hypersensitivity to any active substance or excipient of CLTX-305 (encaleret)

-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

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Roberts MS, Gafni RI, Brillante B, Guthrie LC, Streit J, Gash D, Gelb J, Krusinska E, Brennan SC, Schepelmann M, Riccardi D, Bin Khayat ME, Ward DT, Nemeth EF, Rosskamp R, Collins MT. Treatment of Autosomal Dominant Hypocalcemia Type 1 With the Calcilytic NPSP795 (SHP635). J Bone Miner Res. 2019 Sep;34(9):1609-1618. doi: 10.1002/jbmr.3747. Epub 2019 Jul 26. PMID: 31063613; PMCID: PMC6744344.

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Principal Investigator

Referral Contact

For more information:

Rachel I. Gafni, M.D.
National Institute of Dental And Craniofacial Research (NIDCR)
NIHBC 30 BG RM 218
(301) 594-9924

Karen A. Pozo, R.N.
National Institute of Dental And Craniofacial Research (NIDCR)
National Institutes of Health
Building 10
Room 1N103
10 Center Drive
Bethesda, Maryland 20892
(301) 827-1138

Office of Patient Recruitment
National Institutes of Health Clinical Center (CC)
Building 61, 10 Cloister Court
Bethesda, Maryland 20892
Toll Free: 1-800-411-1222
Local Phone: 301-451-4383
TTY: TTY Users Dial 7-1-1

Clinical Trials Number:


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