Calcitriol (vitamin D therapy) is still a somewhat controversial treatment, although advocated by some veterinarians.
 

The rationale for its use is that it is an effective treatment for renal secondary hyperparathyroidism (over-production of parathyroid hormone caused by kidney failure), which may play an important role in the removal of waste products from the body, and possibly the progression of renal failure.
 

Controlled studies to substantiate a beneficial role for this therapy are lacking and further studies are necessary before it can receive strong recommendation.