The primary objective was to assess the safety and tolerability of cinacalcet in adults with primary hyperparathyroidism (HPT) when administered as a single oral once daily doses for 6 consecutive weeks and twice daily for 15 consecutive days.

Inclusion Criteria:

1. Males and females ≥ 18 years of age at screening. In Part 1, females must be postmenopausal (at least 12 months since last menstrual period) or surgically sterile.

   In Part 2, all qualified females replacing a Part 1 subject (i.e., naïve subjects), regardless of reproductive status, may participate if, in the opinion of the principal investigator, an appropriate effective contraceptive method is used throughout the study. All females must have a negative serum pregnancy test within 28 days prior to Baseline (Parts 1 and 2).

2. Men and women participating in this study must agree to use, in the opinion of the principal investigator, highly effective contraceptive measures throughout the study. All females who are pregnant or breast-feeding are excluded. All subjects must notify the principal investigator if they or their partner suspects a pregnancy.

3. Diagnosis of primary HPT. A plasma intact PTH concentration ≥ 45 pg/mL on at least two occasions at least 1 week apart during the 12 months prior to baseline (at least one of these determinations should be made during screening), and a corrected total serum calcium concentration (for each 1 g/dL decrease in albumin level below 4.0 g/dL, the calcium value should be increased by 0.8 mg/dL) greater than the upper limit of normal, but no greater than 12.5 mg/dL.

4. Acceptable renal function, with an estimated creatinine clearance > 50 ml/min as determined by the Cockroft and Gault equation.

5. Acceptable hepatic function, defined as serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and total bilirubin < 2 times the upper limit of normal.

6. Fasting (8 hours) serum glucose ≤ 130 mg/dL and hemoglobin Alc within the central laboratory's normal range.

7. Hematology panel, serum clinical chemistry and urinalysis results within normal ranges

8. Chest x-ray without evidence of active, infectious, inflammatory or malignant process.

Exclusion Criteria:

1. Any unstable medical condition, defined as having been hospitalized within 28 at prior to baseline, or otherwise unstable in the judgement of the investigator.
2. Received within 21 day prior to baseline, therapy with systemic glucocorticoids, lithium, tricyclic antidepressants, thioridazine, haloperidol, flecainide, or other drugs with a narrow therapeutic index that are primarily metabolized by hepatic cytochrome P450 CYP 2D6, drugs that affect renal tubular calcium handling (e.g. thiazide or loop diuretics), and drugs that affect bone metabolism (e.g. calcitonin, selective estrogen receptor modulators [SERMs])
3. Received, within 90 days prior to Baseline, chronic therapy with bisphosphonates or fluoride.
4. Known alcohol abuse, or use of illicit drugs, within 12 months prior to Baseline
5. Experienced a myocardial infarction (MI) within 6 months prior to Baseline
6. A ventricular rhythm disturbance requiring current treatment
7. Received investigational drugs within 28 days prior to Baseline
8. A history of seizures within 12 months prior to Baseline
9. A history (within 5 years) of malignancy of any type, other than nonmelanomatous skin cancers or in situ cervical cancer
10. A gastrointestinal disorder that may be associated with impaired absorption of orally administered medications
11. A Body Mass Index (BMI) < 15 or > 40, obtained during screening
12. An inability to swallow capsules
13. Sarcoidosis, tuberculosis, or other diseases known to cause hypercalcemia
14. Fasting spot urine calcium/creatinine ratio (mg) < 0.05
15. A psychiatric disorder that would interfere with understanding and giving informed consent or compliance with protocol requirements
16. Any other condition that might reduce the chance of obtaining data (eg, known poor compliance) required by the protocol or that might compromise the ability to give truly informed consent.
17. For Part 2, a subject from Part 1 who discontinued treatment early