A Phase 4 Pharmacokinetic Study of Hectorol Injection and Zemplar Injection in CKD Subjects on Hemodialysis

Inclusion Criteria: * The subject must be receiving hemodialysis three times per week for a minimum of three months. * The subject must be receiving intravenous doxercalciferol or paricalcitol at each dialysis session (three times weekly) for a minimum of 12 weeks prior to Screening. * At Screening Visit the subject's laboratory measurements must be within the following ranges: Serum iPTH measurement between 150-800 pg/mL; Corrected calcium measurement ≤ 10.5 mg/dL; Serum phosphorus measurement ≤ 7 mg/dL Exclusion Criteria: * Any ongoing use of over the counter or prescription vitamin D preparations except doxercalciferol or paricalcitol injection or multivitamins. * History of heparin-induced thrombocytopenia.