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.