Effects of intravenous and oral OCT on secondary hyperparathyroidism in dogs with chronic renal failure

: In this study, we compare the relative potency of single intravenous OCT (IV OCT) and 1,25 (OH) (2)D(3) [IV 1,25 (OH) (2)D(3)] on serum PTH and ionized calcium (ICa) in dogs with chronic renal failure (CRF). In addition, we examine the efficacy of intermittent IV OCT. A single dose of OCT (5 microg/kg) to uremic dogs suppressed PTH by 81% without a statistical significant change in serum I Ca. On the other hand, any of the effective doses of 1,25 (OH) (2)D(3) on PTH suppression were hypercalcemic. The intermittent administration of OCT (0.1 microg/kg) or 1,25 (OH) (2)D(3) (0.025 microg/kg), 3 times per week IV suppressed serum PTH by 83% or 77%, relatively without hypercalcemia. To evaluate OCT as an oral drag, it was given intermittently (3 times per week) to a group of 6 uremic dogs for a period of 4 weeks. Subsequently it was changed to a daily administration (0.05 microg/kg) for a period of 2 weeks. Finally the dose was reducted to 0.025 microg/kg. Daily OCT 0.05 microg/kg suppressed serum PTH by 67%. Subsequently 0.025 micro/kg maintained serum PTH within the normal range without hypercalcemia for 4 weeks. OCT seems to be promising as a useful agent not only for hemodialysis patients but also for predialysis and CAPD patients. In conclusion, our results suggest that OCT is a useful vitamin D(3) analogue, which has a potentially larger therapeutic window than that of 1,25 (OH) (2)D(3) and which is available for IV/oral, for the management of secondary hyperparathyroidism.