In Reply.—The question raised about the biological activity of the calcitriol preparation we used is a very important one. The product used in our study was tested in rats and was shown to promote intestinal calcium transport and to increase the bone mineral index (Ross Laboratories, Columbus, Ohio, written communication, April 1980). This calcitriol preparation was also used in a study of patients with chronic renal insufficiency.1 In these patients, both oral and intravenous calcitriol administration raised serum calcium concentrations, and intravenous but not oral calcitriol administration resulted in the suppression of serum parathyroid hormone concentrations. Also, in preterm neonates, 4 μg/Kg of calcitriol has been shown to raise serum calcium and serum osteo-calcin concentrations.2
While the administration of ethiofos has been reported to induce hypocalcemia and suppress serum parathyroid hormone, calcitriol administration has been reported to raise serum calcium concentrations.1,2 However, in preterm neonates in