NATIONAL HARBOR, Md.—Levels of 25-hydroxyvitamin D (25D) higher than 20 ng/mL would be required to normalize intact parathyroid hormone (iPTH) in patients with stages 3 and 4 chronic kidney disease (CKD) with vitamin D insufficiency and secondary hyperparathyroidism, researchers concluded in a study presented at the National Kidney Foundation 2012 Spring Clinical Meetings.

Researchers noted that the Institute of Medicine recently suggested 20 ng/mL as the lower limit of the normal range for 25D, but this limit may be significantly higher among individuals with reduced kidney function.

The investigators examined the relationship between iPTH and 25D in patients with stages 3 and 4 CKD in a double-blind study of CTAP101 Capsules, a modified-release formulation of calcifediol. Seventy-eight patients aged 18-80 years were randomized to receive the capsules or matching placebo for six weeks. At baseline, subjects had a mean eGFR of 39.4 mL/min/1.73 m2, iPTH of 136 pg/mL, 25D level of 22.4 ng/mL, serum calcium level, 9.3 mg/dL, and serum phosphorus level of 3.7 mg/dL.

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In the active drug group, a 25D level of 84 ng/mL was associated with the upper limit of normal for iPTH (72 pg/mL). Some patients had 25D increases exceeding 100 ng/mL, but investigators reported observing no significant change in calcium or phosphorus.