Influence of serum phosphate on the efficacy of oral 1,25-dihydroxyvitamin D3 pulse therapy
Shoji, S.; Nishizawa, Y.; Tabata, T.; Emoto, M.; Morita, A.; Goto, H.; Ishimaura, E.; Inoue, T.; Inaba, M.; Miki, T.
Mineral and Electrolyte Metabolism 21(1-3): 223-228
1995
ISSN/ISBN: 0378-0392 PMID: 7565454 Document Number: 453305
In patients with a moderate degree of renal insufficiency, restriction of dietary phosphate suppresses PTH secretion by increasing serum calcitriol. However, this mechanism may not operate in advanced renal failure. The present study was designed to evaluate the influence of serum phosphate levels on PTH secretion in oral 1,25-dihydroxyvitamin D-3 (1,25(OH)-2D-3) pulse therapy. 22 patients with secondary hyperparathyroidism (carboxy-terminal PTH (c-PTH) concentration: 19.5 +- 13.9 ng/ml, mean +- SD) received oral doses of 1,25(OH)-2D-3 (3.0-4.0 mu-g) twice a week, each at the end of hemodialysis, for 12 weeks. Doses of phosphate binders remained unchanged throughout this period. Patients were divided into two groups: group A (11 subjects) with mean serum phosphate levels of less than 6.0 mg/dl and group B (11 subjects) with levels of 6.0 mg/dl and above. There was no significant difference in the average corrected serum calcium levels. The reduction in serum intact PTH levels was greater in group A than in group B. A negative correlation (r = -0.48; p lt 0.05) was observed between mean serum phosphate levels and the percent decrease in serum c-PTH levels. The findings of this study indicate an important role for dietary phosphate reduction in oral 1,25(OH)-2D-3 pulse therapy and suggest that serum phosphate reduction may play a part in suppressing PTH secretion through a mechanism independent of 1,25(OH)-2D-3 and plasma calcium levels.