Relationship between urinary calcium and calcium intake during calcitriol administration

Calcium balance in normal individuals and in patients with chronic kidney disease on low- and high-calcium diets

Calcium balance in chronic kidney disease is poorly understood since its deficiency is a stimulus for secondary hyperparathyroidism and consequent bone loss while calcium excess promotes extra-osseous calcifications. To help resolve this, we evaluated calcium balance in normal individuals and in patients with chronic kidney disease (CKD) on daily diets containing 800 and 2000 mg elemental calcium. Both normal individuals and patients with late stage 3 and stage 4 CKD were in slightly negative to neutral calcium balance on the 800 mg calcium diet. Normal individuals were in modest positive calcium balance on the 2000 mg diet while patients with CKD on the same diet were in marked positive calcium balance at least over the 9 days of study; and significantly greater than the normal individuals. Increased calcium intake significantly decreased 1,25 dihydroxy-vitamin D and intact parathyroid hormone levels but did not alter the serum calcium concentration. Thus, our finding have important implications for both preventing calcium deficiency and loading in individuals with late stage 3 and stage 4 CKD.

Doxercalciferol safely suppresses PTH levels in patients with secondary hyperparathyroidism associated with chronic kidney disease stages 3 and 4

BACKGROUND

Calcitriol lowers parathyroid hormone (PTH) levels in patients with chronic kidney disease (CKD) stages 3 and 4, but its use is limited by a low therapeutic index and concerns regarding hypercalcemia and acceleration of kidney disease. We evaluated doxercalciferol (1alpha-hydroxyvitamin D2) as an alternative therapy in a randomized, double-blinded, placebo-controlled, multicenter trial.

METHODS

Fifty-five adults with stage 3 or 4 CKD and an intact PTH (iPTH) level greater than 85 pg/mL (ng/L) completed 8 baseline weeks, followed by 24 weeks of oral therapy with doxercalciferol or placebo. Pretreatment demographics and biochemical features did not differ between groups. Dosages were increased gradually if iPTH level was not decreased by 30% or greater and serum calcium and phosphorus levels were stable. Regular monitoring included plasma iPTH, serum calcium and phosphorus, urinary calcium, bone-specific serum markers, and serum lalpha,25-dihydroxyvitamin D levels. Glomerular filtration rate (GFR) was measured before and after treatment.

RESULTS

Mean plasma iPTH level decreased by 46% from baseline after 24 weeks of doxercalciferol treatment (P <0.001), but was unchanged with placebo. After 6 weeks, iPTH level reductions with doxercalciferol treatment exceeded those with placebo at all subsequent intervals (P <0.001). No clinically significant differences in mean serum calcium or phosphorus or urinary calcium levels or incidence of hypercalcemia, hyperphosphatemia, or hypercalciuria were noted between groups. Serum C- and N-telopeptide and bone-specific alkaline phosphatase levels decreased with doxercalciferol treatment relative to both baseline and placebo (P <0.01). Adverse-event rates and changes in GFR did not differ between groups.

CONCLUSION

Doxercalciferol is safe and effective in controlling secondary hyperparathyroidism of patients with CKD stages 3 and 4.

Biochemical responses to sequential human parathyroid hormone (1-38) and calcitonin in osteoporotic patients

Parathyroid hormone (PTH) has been proposed as a skeletal activator for cyclical protocols of treatment for osteoporosis; among several potential drugs that might serve to depress the subsequent phase of osteoclastic bone resorption, calcitonin is the most selective. Twenty patients aged 50-78 years were enrolled in a study of their biochemical responses during a 14-day activation cycle with synthetic hPTH 1-38, given as a subcutaneous injection of 400 IU/day; half the patients were randomly allocated to receive a subsequent 56-day depressor cycle with calcitonin in a dose of 100 U/day, while the remainder received no further treatment. All patients received an initial 24-h intravenous infusion of hPTH 1-38 (0.5 U/kg/h) to evaluate the PTH-dependent renal synthesis of 1,25(OH)2D. Serum calcium increased from 2.20 +/- 0.07 mmol/l to 2.56 +/- 0.16 (P less than 0.005) during PTH infusion, but was not significantly different from baseline during intermittent treatment. Baseline concentrations of serum 1,25(OH)2D were 22.8 +/- 8.2 pg/ml, increased to 52.2 +/- 25.1 (P less than 0.005) during infusion and remained significantly higher than baseline after 14 days intermittent therapy (33.1 +/- 19.4, P less than 0.05). Gastrointestinal absorption of 45Ca, as represented by alpha (peak fractional absorption/h), increased from 0.397 +/- 0.173 to 0.552 +/- 0.210 (P less than 0.01) during hPTH 1-38 therapy and was moderately correlated with the increment in serum 1,25(OH)2D levels (r = 0.5, P less than 0.03). Daily calcium excretion was significantly increased above baseline during hPTH 1-38 therapy, but there were no correlations between changes in urinary calcium, alpha or serum 1,25(OH)2D levels. Baseline fasting urinary excretion of OH-proline increased during hPTH 1-38 treatment from 30.5 +/- 13.9 mol/mmol creatinine to 43.4 +/- 17.5 immediately after hPTH 1-38 infusion (P less than 0.025), and mean excretion was persistently higher than baseline during intermittent treatment; the increased urine calcium and OH-proline excretion are consistent with PTH-induced activation of bone resorption. Serum alkaline phosphatase and osteocalcin levels increased significantly during a 90-day period of observation after the hPTH 1-38 cycle, which is consistent with increased osteoblast activity in association with coupled bone formation.(ABSTRACT TRUNCATED AT 400 WORDS)