Sir.—I read with interest the article by Venkataraman et al1 in the October issue of AJDC. After reading their explanations and examining Fig 2, which did not indicate any dose-dependent calcium response to parenteral administration of 1,25-dihydroxyvitamin D, I wonder about the biological activity of the calcitriol that the authors used.
I was also struck that the parathyroid hormone levels of the infants did not seem to respond at all to hypocalcemia, although markedly low calcium levels (such as 1.01 mmol/L [4.03 mg/dL]) were recorded. There was also no mention of the observation of tetany in these infants. These findings may suggest the inhibition of parathyroid hormone secretion in these infants, as is observed with administration of ethiofos (WR 2721),2 or acceptance of early neonatal hypocalcemia as a physiologic phenomenon that does not require treatment, as proposed by Scott et al.3 However, the determination of ionized
Özsoylu Ş. Biological Activity of Calcitriol. Am J Dis Child. 1987;141(10):1039. doi:10.1001/archpedi.1987.04460100017006
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