The purpose of this study is to evaluate the effects of Zemplar® Injection and Hectorol® Injection on intestinal calcium absorption in Chronic Kidney Disease Stage 5 subjects on hemodialysis.

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.