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- See:
      - abnormalities associated w/ vit D
      - general discussion of vit D

- Discussion:
    - action of l,25-vitamin D3 is to increase absorption of Ca from intestinal tract;
    - 1,25 Vit D is known mediator of bone resorption thru indirect action on osteoclasts;
    - amount of this metabolite in circulation is regulated by parathyroid hormone;
    - malfunctions involving this metabolite are a major cause of metabolic bone dz;

- Dosage:
    - most potent metabolite of vitamin D available;
    - used for hypocalcemia secondary to chronic renal dialysis, post surgical and idiopathic hypoparathyroidism;
    - dialysis patients:
          - initial dose is 0.25ug/day; may increase dosage by 0.25ug/day at 4-8 week intervals if needed;
          - max dose: 100 mcg qd (available as 20 and 50 mcg);
    - hypoparathyroidism: initial dose is 0.25ug/day given AM;
    - may increase dose at 2-4 week intervals;
    - contraindicated w/: hypercalcemia, evidence of vit D toxicity;
    - must monitor calcium levels frequently;
    - caution w/ digitalis (w/ hypercalcemia) and attempt to maintain good fluid intake;
    - note: when Vit D is measured in units it is in the non hydroxylated form, and when it is measured in micrograms (Rocaltrol) it is in the hydroxylated form (1,25 Vit D)