CALCITRIOL THERAPY IN PREDIALYTIC SECONDARY HYPERPARATHYROIDISM - EFFECTS OF ORAL PULSES VERSUS A DAILY ORAL REGIMEN

Secondary hyperparathyroidism develops very early in the course of chr onic renal failure and the reduced availability of calcitriol is a maj or pathogenic factor. A randomized cross-over study was planned to com pare the suppressive effect of daily oral or oral pulse calcitriol th erapy on parathyroid response. Sixteen patients with advanced predialy tic renal failure (creatinine clearance between 7 and 25 ml/min) were treated for seven months with daily oral calcitriol (0.5-1 mu g/day) a nd pulse doses of oral calcitriol (2 mu g/day three times a week) sepa rated by a four-week wash-out period. A three-hour intravenous calcium suppression test was done at the beginning and end of each treatment period, resulting in the generation of parathyroid hormone/ionized cal cium (PTHi/iCa) relationship curves. PTHi levels were reduced by over 50% (from 201 +/- 102 pg/ml to 99 +/- 94; p=0.01) by the oral pulse th erapy with a leftward and downward shift of the PTHi/Ca relationship c urve and an important decrease in iCa for any given PTHi value. Daily oral calcitriol was ineffective in reducing PTHi values, inducing only a slight increase of plasma ionized calcium (from 1.15 to 1.19 mMol/l ). No significant changes in serum levels of bone GLA. and procollagen I and III were detected throughout the treatment period.