It's spelled Rocaltrol (also known as Calcijex.) From Mosby's Medical Drug reference:
Active in regulation of the absorption of calcium from the gastrointestinal tract and it's utililization in the body; increases renal tubular resorption of phosphate.
They are apparently concerned about low calcium and resultant metabolic bone disease.
Do you have a go-to person on the transplant team, such as a coordinator or P.A., that you could call and ask about the megadose Vit. A?