Studies With 1,25-Dihydroxycholecalciferol

Patients with extreme resistance to 1,25-dihydroxyvitamin D will be evaluated and treated with high doses of 1,25-dihydroxyvitamin D3.

Plan: In previously untreated patients the study will be divided into a control and one or more treatment periods. During the control period, parathyroid status will be assessed by parameters nos. 1& 2 (below). In previously treated patients maintenance vitamin D will be gradually replaced with 1,25(OH)2D3. This will be accomplished by withdrawal of vitamin D and institution of 1,25(OH)2D3 when the serum calcium shows a downward trend.

1,25(OH)2D3 as 0.25 or 0.5 ug capsules (though IND 20,889) or as a solution of I microgram per ml will be administered orally. In most cases, because of consideration of time and expense, the cooperation of the patient's local physician will be enlisted. The following will be monitored:

1. Serum calcium, phosphorus,alkaline phosphatase,creatinine at twice weekly intervals. After a maintenance dose has been established, this will be decreased to a monthly, and subsequently 3-6 monthly interval.
2. Urine calcium, phosphorus,creatinine and cAMP before therapy and, when appropriate, during therapy.

The dose of 1,25(OH)2D3 will be 0.125 to 50.0 ug/day. Serum calcium will not be allowed to rise above the normal range (2.0 -2.4 mM at NIH). Should hypercalcemia occur, appropriate treatment will be initiated and the drug dosage will be decreased.