A Study of Zemplar® Injection and Hectorol® Injection on Intestinal Absorption of Calcium in Chronic Kidney Disease

Inclusion Criteria: Subject is >= 20 years of age. Subject is diagnosed with CKD Stage 5, and must be on maintenance (chronic) hemodialysis (HD) three times a week for at least 2 months prior to the Screening Visit and expected to remain on HD for the duration of the study. If female, subject is either not of childbearing potential, defined as postmenopausal for at least 1 year or surgically sterile (bilateral tubal ligation, bilateral oophorectomy or hysterectomy), or is of childbearing potential and practicing one of the following methods of birth control: Condoms, sponge, foams, jellies, diaphragm or intrauterine device (IUD) Contraceptives (oral or parenteral) for three months prior to study drug administration In a monogamous relationship with a vasectomized partner If female, subject is not breastfeeding and has a negative serum pregnancy test prior to the treatment phase. Subject has an intact PTH value > 200 pg/mL at Screening only (or Re-screening, if applicable). Subject has a serum calcium level < 10.2 mg/dL at Screening only (or Re-screening, if applicable). Subject has a serum phosphorus level < 6.5 mg/dL at Screening only (or Re-screening, if applicable). Subject has a CaxP product <= 65 at Screening only (or Re-screening, if applicable). Subject must voluntarily sign and date an informed consent, approved by an Institutional Review Board (IRB)/Independent Ethics Committee (IEC), prior to the conduct of any study-specific procedure. Exclusion Criteria: Subject has a history of an allergic reaction or significant sensitivity to vitamin D or vitamin D related compounds. Subject has chronic gastrointestinal disease, which in the Investigator's opinion, may result in clinically significant GI malabsorption. Liver function defects defined as > 2 times the upper limit of normal for liver enzyme (SGOT/AST, SGPT/ALT) levels. Subject has a hemoglobin level < 9.0 g/dL. Subject is taking maintenance calcitonin, Sensipar® (cinacalcet), glucocorticoids in an equivalent dose > 5 mg prednisone daily, or other drugs that may affect calcium or bone metabolism within 2 weeks prior to screening, other than females on stable (same dose and product for 3 months) estrogen and/or progestin therapy. For any reason, subject is considered by the Investigator to be an unsuitable candidate to receive pharmacological doses of vitamin D. Subject has received any investigational drug within 4 weeks prior to the Treatment Phase.