Variation in Oral Calcitriol Response in Patients With Stages 3-4 CKD

Background

Oral calcitriol decreases parathyroid hormone (PTH) concentrations in patients who have chronic kidney disease (CKD); however, treatment response is highly variable. We evaluated whether patient characteristics affect the PTH response to oral calcitriol in nondialysis patients with CKD in a clinic-based setting.

Study Design

Cohort study.

Setting & Participants

This study included 379 new oral calcitriol users in the Veterans' Affairs Northwest Health Network. All had stages 3-4 CKD, hyperparathyroidism, and a serum PTH measurement before and 1-6 months after initiating oral calcitriol therapy.

Predictors

Patient-level characteristics hypothesized to affect calcitriol response: race, body size, concurrent medications, and kidney function.

Outcomes

Relative decrease in serum PTH concentration after starting oral calcitriol therapy.

Measurements

Data were abstracted from the Veterans' Affairs Northwest Health Network (VISN 20) Data Warehouse, which includes electronic pharmacy and laboratory records.

Results

Mean estimated glomerular filtration rate was 30 mL/min/1.73 m² and mean initial PTH concentration was 199 pg/mL. Regular- (0.25 μg/d) and low-dose (<0.25 μg/d) oral calcitriol were associated with on average 23% and 13% relative decreases in serum PTH concentrations, respectively. After adjustment for calcitriol dosage, initial PTH concentration, and time to follow-up measurement, African American race was associated with a blunted calcitriol response (geometric mean final PTH value, 26% higher; 95% CI, 8%-47%). Serum albumin concentration <3.5 g/dL also was associated with a diminished calcitriol response (geometric mean final PTH, 19% higher; 95% CI, 6%-35%). Although numbers were small, concurrent use of benzodiazepines and nonactivated vitamin D supplements was associated with a significantly greater PTH response.

Limitations

Clinic-based study is limited by the availability of PTH measurements after starting calcitriol therapy. Study of a predominantly older male population.

Conclusions

In patients with stages 3-4 CKD, African American race and low serum albumin level are associated with a diminished PTH response to oral calcitriol.

Index Words:  Activated vitamin D , calcitriol , parathyroid hormone , hyperparathyroidism , drug metabolism