Please select the eligibility criteria that correspond to the clinical trial below.
Title: Analysis of Calcium Balance in Chronic Kidney Disease
Brief Summary: Subjects with normal kidney function are able to excrete in their urine the calcium and phosphorus absorbed via the gastrointestinal tract and are thereby are able to maintain calcium and phosphorus balance. Patients with chronic kidney disease often have normal blood levels of calcium and phosphorus but no research has been conducted to determine if they are able to excrete their daily intake of these minerals. If they are not able to excrete their daily intake, these minerals could be deposited in soft tissue and blood vessels and contribute to the increased risk of cardiovascular disease seen in patients with chronic kidney disease. This study will determine if subjects with chronic kidney disease are in balance primarily with regard to calcium and at what level of kidney function they are no longer able to maintain balance. Understanding whether patients with chronic kidney disease are in balance will help direct future therapeutic interventions.


Options:
A: Inclusion Criteria:

1. Patients with a GFR of \< 45 ml/min;
2. Intact serum PTH \> 37 pg/ml;
3. Age \> 35 years (both genders and all races);
4. Able to perform two three-week balance studies;
5. Not on oral calcium or vitamin D other than multi vitamin, or willing to stop calcium or vitamin D for one month prior to entry in the study (day 1 of first calcium balance period);
6. Female patients must be post-menopausal (defined as last menstrual period at least 12 months prior to screening visit) or surgically sterile by hysterectomy;
7. On stable doses of diuretics, bisphosphonates, anti-epileptics (except dilantin) for at least 2 months.

Exclusion Criteria:

1. Serious underlying systemic disease (including uncontrolled diabetes, lupus, hypertension, amyloid, etc);
2. Taking drugs that alter calcium and phosphate balance or homeostasis including high dose cholecalciferol or ergocalciferol (1000 U/day or 50,000U/ wk, respectively), active vitamin D metabolites, calcimimetics, PTH analogues in the last 30 days;
3. Taking drugs that the investigator feels will alter calcium balance;
4. Plan to initiate dialysis in the next six months;
5. Hypercalcemia defined as serum calcium \> 10.5 mg/dl;
6. Hyperphosphatemia defined as serum phosphate \>5.5mg/ml;
7. Intestinal disease that alters absorption or normal intestinal function including celiac disease, small bowel resection, bariatric surgery;
8. Smoking
B: Inclusion Criteria:

* Age \> 18 years
* Capable of giving informed consent
* Duration of peritoneal dialysis \> 3 months
* Dose of phosphate binder(s) stable over previous 2 week period
* Plasma phosphours \> 4.9 mg/dL based on most recent laboratory data within 1 month of enrollment

Exclusion Criteria:

* Pregnancy
* Known liver disease
* Active peptic ulcer disease
* Treatment with carbamazepine
* Intolerance to niacinamide or niacin
* Current medication regimen including niacin or niacinamide \> 100 mg daily
* Planned or expected surgical procedure in the next 4 months
* Patients in nursing home or extended care facilities where administration of the study drug may not be appropriately given
C: Inclusion Criteria:

* Written informed consent given
* Able to comply with the study procedures and medication
* On a stable HD regimen (at least 3 x per week) for ≥ 3 months
* Subject receiving calcium carbonate or sevelamer hydrochloride as a phosphate binder at screening, must have been on a stable regimen (dose and medication) for at least 1 month
* A mean serum inorganic phosphorous in the previous 3 tests : \> 5.5 mg/dL and \< 9.0 mg/dL
* Removal rate of blood urea nitrogen (BUN) ≥ 60%
* Rate of salivary flow by Saxon test ≥ 1 g/2 min

Exclusion Criteria:

* Blood purification therapy other than HD
* Current clinically significant intestinal motility disorder
* Possible parathyroid intervention during the study period
* History of malignancy and severe cardiovascular disorders such as heart disease, angina, congested heart failure, valve stenosis, atrial fibrillation and arrhythmia
* History of allergy against active ingredient
* Receipt of any investigational drug within 30 days of informed consent
D: Inclusion Criteria:

* Men and women 18 years of age or greater and able to comply with the study protocol.
* eGFR within appropriate target ranges (15-40 ml/min/m² for late stage CKD stage 3 stage 4, and eGFR \> 60 ml/min/m² for normal subjects)
* Stable kidney function defined as an eGFR which remains within a 10ml/min range over a 3 to 6 month period prior to study enrollment. This will be determined from historical laboratory data.
* Willing to follow study protocol
* Have a level of understanding and willingness to cooperate with all visits and procedures as described by the study personnel
* Overall stable medical condition, defined as no malignancy, metabolic condition or gastrointestinal condition that would make it difficult to comply with the study protocol and complete both dietary study periods
* Able to read the consent form and provide informed consent.
* Serum calcium and phosphorus within the normal range off of vitamin D analogues, calcium supplements, and phosphate binders for 1 month.

Exclusion Criteria:

* 1. Age less than 18 years
* Are pregnant, plan on becoming pregnant during the study period, or breast-feeding, if female.
* Patient declines participation.
* GI malabsorption, short bowel syndrome, frequent vomiting, or gastroparesis.
* Subject receiving synthetic parathyroid hormone, glucocorticoids, calcitonin or bisphosphonates.

Answer: D