COMPARISON OF THE BIOLOGICAL EFFECTIVENESS OF CALCITRIOL AND DIHYDROTACHYSTEROL

Calcitriol and dihydrotachysterol are both used in clinical practice a s treatment for several renal and endocrine conditions. However, despi te their routine use, therapeutic dosages and concomitant adverse effe cts of these medications have yet to be clarified. In our study, a low , high and extreme dosage of calcitriol (20, 60, 120 ng/kg/day) or dih ydrotachysterol (15, 45, 90 mu g/kg/day) was administered to six group s of male Sprague Dawley rats for four weeks. The seventh group served as untreated controls. Our results indicated no difference in food in take, weight gain, or total or ionized plasma calcium among treatment groups. Rats receiving 90 mu g/kg/day dihydrotachysterol excreted more calcium than those receiving 120 ng/kg/day calcitriol (p < 0.002). Fe mur and kidney calcium showed no significant differences for any dosag es used of either medication. Mean urine calcium was significantly cor related with ionized plasma calcium (p < 0.006) and kidney calcium (p < 0.02). Light microscopy revealed evidence of calcification in one ra t out of six receiving the extreme dose (120 ng/kg/day) of calcitriol and one rat out of six receiving the extreme dose (90 mu g/kg/day) of dihydrotachysterol. These results suggest that serum and urine calcium must be carefully monitored during either form of vitamin D therapy, but no effect on calcium content or histology of the kidneys was obser ved in the common therapeutic range.