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 pro…