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

Inclusion Criteria

• Patients with a GFR of 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