Differences in the bioavailability of dihydrotachysterol preparations.

The bioavailability of four preparations containing dihydrotachysterol (DHT2) was tested in two separate trials with administration of single, oral doses of 1 mg per individual. The relative bioavailability of corresponding preparations (capsules vs capsules and oral solution vs oral solution) was tested in a randomised, cross-over pattern within the same group of volunteers. Two different groups of 24 healthy volunteers took part in each trial. Solution and capsule bioavailability was also compared inter-individually. A new sensitive HPLC-method (quantification limit 0.5 ng.ml-1) was used for the measurement of DHT2 concentration in serum. Three of the preparations tested had a similar bioavailability (mean AUC values of 195.5-223 ng.h.ml-1); the bioavailability of the fourth preparation (A.T.10 oral solution) was considerably lower (mean AUC value 111.5 ng.h.ml-1). The present dosage recommendations of all four preparations are identical. A new dosage recommendation is thus required for the oral solution with low bioavailability (A.T.10).

Action and metabolism of dihydrotachysterol2.

Dihydrotachysterol2 (DHT2) is a synthetic analogue of vitamin D2. DHT2 is used extensively in the treatment of renal osteodystrophy and hypoparathyroidism. It is equally efficacious as 1 alpha,25-dihydroxyvitamin D3 and 1 alpha-hydroxyvitamin D3. Moreover, it offers interesting therapeutical advantages and it is surprising that until recently little was known of its metabolism and sites of action. This paper deals with studies on the pharmacology of DHT2 in rats. Following the synthesis of [3H]DHT2 and oral administration, evidence was obtained that DHT2 is metabolized extensively; three of the major metabolites could be identified as 25-hydroxy-DHT2, 1 alpha,25- and 1 beta,25-dihydroxy-DHT2.