Effects of subcutaneous calcitriol administration on plasma calcium and parathyroid hormone concentrations in continuous ambulatory peritoneal dialysis uremic patients.

OBJECTIVE To ascertain whether the parathyroid hormone (PTH) secretion of continuous ambulatory peritoneal dialysis (CAPD) uremic patients could be suppressed by repeated subcutaneous injections of calcitriol (CLT). DESIGN Nonrandomized prospective study with weekly evaluation. SETTING Hospital CAPD clinic. PATIENTS Seven uremic CAPD patients with signs of severe hyperparathyroidism. INTERVENTIONS Patients were treated with CLT (2 micrograms), injected subcutaneously three times a week, on alternate days over a period of 8 weeks. MEASUREMENTS Plasma PTH, ionized calcium (Ca), serum phosphate (Pi), and alkaline phosphatase (AP) were assayed before the start of CLT therapy and weekly thereafter. RESULTS The average basal PTH was 349 +/- 26 pg/mL (mean +/- SD). It fell significantly by the fifth week to 158 +/- 20, then leveled off. Analysis of the individual data, however, revealed that only 5 of 7 patients had a significant decrease in plasma PTH. Basal Ca was +/- .02 mmol/L; it increased continuously throughout the study, significantly by the fourth week, reaching a level of 1.33 +/- 0.3 mmol/L at the sixth week, then declined slightly. In those patients with significantly decreased PTH, there was an inverse correlation between PTH and the corresponding Ca levels. CONCLUSIONS In some CAPD patients subcutaneous administration of CLT significantly suppresses PTH. This effect is mainly mediated via an increase in ionized calcium, but a direct inhibitory effect of the vitamin on parathyroid glands cannot be excluded.