Inclusion Criteria:

• Under care of physician at least 2 months (for CKD)
• Not on active Vitamin D therapy for at least 4 weeks prior

• If female:

  • Not of childbearing potential, OR
  • Practicing birth control
  • Not breastfeeding
• If taking phosphate binders, on a stable regimen at least 4 weeks prior

• For entry into Pretreatment Phase:

  • iPTH at least 120 pg/mL
  • GFR of 15-60 mL/min and no dialysis expected for at least 6 months

• For entry into Treatment Phase:

  • Average of 2 consecutive iPTH values of at least 150 pg/mL, taken at least 1 day apart (all values not less than 120 pg/mL
  • 2 consecutive corrected serum calcium levels between 8.0-10.0 mg/dL
  • 2 consecutive serum phosphorus levels of not more than 5.2 mg/mL

Exclusion Criteria:

• History of allergic reaction or sensitivity to similar drugs
• Acute Renal Failure within 12 weeks of study
• Chronic gastrointestinal disease
• Spot urine result demonstrating a urine-calcium-to-urine creatinine ratio of greater than 0.2, or a history of renal stones
• Taken aluminum-containing phosphate binders within last 12 weeks, or requires such medication for more than 3 weeks during study
• Current malignancy, or clinically significant liver disease
• Active granulomatous disease (TB, sarcoidosis, etc.)
• History of drug or alcohol abuse within 6 mos. prior
• Evidence of poor compliance with diet or medication
• Received any investigational drug or participated in any device trial within 30 days prior
• Taking maintenance calcitonin, bisphosphonates, or drugs that may affect calcium or bone metabolism (other than females on stable estrogen and/or progestin therapy)
• On glucocorticoids for a period of more than 14 days within the last 6 months
• HIV positive