Calcium and Phosphorus Balance and Calcium Kinetics in Patients With Stage 3/4 Chronic Kidney Disease

Study Overview
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Brief Summary
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The purpose of this study is to gain a better understanding of calcium absorption and metabolism in patients with Chronic Kidney Disease (CKD) using calcium balance and kinetic methods.

Detailed Description
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The purpose of this study is to gain a better understanding of calcium absorption and metabolism in patients with Chronic Kidney Disease (CKD). It is important that the body get enough calcium to support many important body functions including bone health. CKD changes the calcium balance or how calcium is absorbed and excreted. Because of this, the knowledge of calcium absorption and excretion in patients with normal kidney function cannot be used to assess patients with CKD. In patients with CKD bone heath is often negatively affected due to a combination of poor calcium absorption, increased bone turnover (process where old bone is removed and new bone is formed), increased level of parathyroid hormone (PTH [ a hormone that acts to increase calcium in the blood]) and decrease in vitamin D levels. This negative effect is referred to as Chronic Kidney Disease Mineral Bone Disorder (CKD-MBD). Treatment to correct CKD-MBD should begin early in the course of CKD. In the normal population calcium supplements are frequently used to help prevent age related bone loss. Calcium supplements can also be used in CKD patients to help bind phosphate. Maintaining correct levels of phosphate in the body is crucial in CKD. However, calcium supplements may have adverse effects by promoting calcium phosphate deposits in soft tissues like the vascular system which could increase the risk of cardiovascular disease. Therefore this formal balance study is needed to determine if positive calcium balance occurs in patients with advanced CKD who are given calcium with meals as a phosphate binder. This study will also evaluate how the body handles phosphate.

Official Title
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Calcium and Phosphorus Balance and Calcium Kinetics in Patients With Stage 3/4 Chronic Kidney Disease

Conditions
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Chronic Kidney Disease

Intervention / Treatment
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* Dietary Supplement: 1500 mg/d elemental calcium as calcium carbonate
* Dietary Supplement: Placebo


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Patients with a GFR of < 45 ml/min; Intact serum PTH > 37 pg/ml; Age > 35 years (both genders and all races); Able to perform two three-week balance studies; 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); Female patients must be post-menopausal (defined as last menstrual period at least 12 months prior to screening visit) or surgically sterile by hysterectomy; On stable doses of diuretics, bisphosphonates, anti-epileptics (except dilantin) for at least 2 months. Exclusion Criteria: Serious underlying systemic disease (including uncontrolled diabetes, lupus, hypertension, amyloid, etc); 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; Taking drugs that the investigator feels will alter calcium balance; Plan to initiate dialysis in the next six months; Hypercalcemia defined as serum calcium > 10.5 mg/dl; Hyperphosphatemia defined as serum phosphate >5.5mg/ml; Intestinal disease that alters absorption or normal intestinal function including celiac disease, small bowel resection, bariatric surgery; Smoking

Ages Eligible for Study
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Minimum Age: 35 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Quadruple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Placebo Comparator: Placebo<br>Placebo control for calcium carbonate, given in same capsule form as the calcium carbonate, 3 times per day with meals. | Dietary Supplement: Placebo<br>* Placebo for calcium carbonate in same capsule form. Given 3 times per day with meals for 21 days in conjunction with a controlled diet.<br>|
| Active Comparator: Calcium Carbonate (Phosphate Binder)<br>500 mg elemental calcium as calcium carbonate given 3 times per day with meals for a total of 1500 mg/d elemental calcium. | Dietary Supplement: 1500 mg/d elemental calcium as calcium carbonate<br>* 500 mg elemental calcium as calcium carbonate given 3 times per day with meals for a total of 1500 mg/d elemental calcium. Given for 21 days in conjunction with a controlled diet.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Calcium Balance | Calcium balance is measured by dietary calcium intake (mg/d) minus calcium excretion (mg/d) (from both urine and feces). | 2 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Phosphorus Balance | Phosphorus balance is measured by dietary phosphorus intake (mg/d) minus phosphorus excretion (mg/d) from both urine and feces. | 2 weeks | 
| Bone Balance From Calcium Kinetics | Calcium kinetics was determined by a calcium radiotracer. Bone balance is the difference between bone formation and bone resorption estimated by calcium kinetic modeling. | 2 weeks |