Secondary Hyperparathyroidism (SHPT) occurs in many patients with kidney disease and leads to bone disease. Active forms of vitamin D, calcitriol and paricalcitol, treat SHPT, but may have different effects on blood calcium. This study will randomize patients with SHPT and stage 3 or 4 CKD to treatment with calcitriol or paricalcitol, and monitor patients for the incidence of high blood calcium, and effectiveness of SHPT treatment.

General Design

• Open label, active comparator, multicenter, parallel group, phase 4 study of paricalcitol versus calcitriol for suppression of PTH in stage 3 and 4 CKD patients with SHPT.
• Total study duration is 26 weeks (1 week screening, 24 weeks active medications, 1 week follow up.
• Patients meeting inclusion/exclusion criteria including baseline laboratory results will be randomized to paricalcitol or calcitriol, and enter a 24 weeks treatment phase. Visits, including safety and efficacy laboratory tests will be at weeks 4, 8, 12, 18, and 24. A follow up visit will be performed 1 week after stopping study medication.

Inclusion Criteria

1. Age >18; Able to give informed consent
2. Chronic kidney disease, and estimated GFR 15 to 60 ml/min using the abbreviated MDRD equation
3. intact PTH (iPTH) >120 pg/ml at baseline
4. albumin corrected calcium > 8.5 mg/dL to < 10.0 mg/dL at baseline
5. Phosphorus < 4.6 mg/dL at baseline
6. If on a phosphorus binder; no change in dose within the 4 weeks prior to screening

Exclusion Criteria

1. Receiving any active form of vitamin D within 4 weeks prior to screening (calcitriol, doxercalciferol; paricalcitol; alfacalcidol)
2. Receiving >50,000 IU per month of ergocalciferol or > 1000 IU of cholecalciferol per day within the previous 30 days.
3. history of primary HPT
4. On prednisone > 30 days within the previous 6 months
5. receiving bisphosphonates or calcitonin within the previous 12 months
6. Non-elective hospitalization within the previous 30 days.
7. Expected to initiate dialysis or receive a kidney transplant within the next 6 mo.
8. History of renal or other organ transplant
9. History of parathyroidectomy or previous diagnosis of primary hyperparathyroidism
10. Receiving cinacalcet within 4 weeks prior to screening.
11. An active drug/alcohol dependence or abuse history
12. History of non-compliance with visits or medications that preclude study compliance in the opinion of the investigator
13. Pregnant, or able to become pregnant and unwilling to use a birth control method considered reliable by the principal investigator