A possible direct effect of 24,25-dihydroxycholecalciferol on the parathyroid gland in patients with chronic renal failure.

Seventeen undialysed adult patients with chronic renal failure took part in a controlled study of the effects of 1,25(OH)2D3 and D3. After a 6-month observation period the patients were allocated at random to two groups for 6 months of treatment with either 1,25(OH)2D3 (mean dose 0.5 microgram daily) or D3 (dose 100 microgram daily). The treatment was then discontinued and the patients were studied for a further 3 months. In the 1,25(OH)2D3 group the mean serum concentration of 1,25(OH)2D rose significantly during treatment, whereas serum concentratins of 25OHD and 24,25(OH)2D remained unchanged. In the D3 group there was a highly significant increase in serum concentrations of 25OHD and 24,25(OH)2D, whereas serum 1,25(OH)2D remained unchanged. There was a significant fall in serum iPTH in both treatment groups. This fall was unrelated to serum calcium in the D3 group unlike the findings in the 1,25(OH)2D3 group. The data support previous experimental evidence that serum iPTH can be suppressed by 24,25(OH)2D3 and suggest that this analogue may be of clinical importance in the treatment of chronic renal failure without inducing hypercalcaemia.