Successful off-label use of cinacalcet HCl after standard therapy failure in a young man with pseudohypoparathyroidism Type 1b and vitamin D intoxication sequelae.

We describe the case of a young man with pseudohypoparathyroidism Type 1b--a rare genetic disorder characterized by end-organ resistance to parathormone (PTH)--and vitamin D intoxication sequelae due to inappropriate and poorly monitored calcitriol treatment in his adolescence, who could no longer be successfully treated by standard vitamin D treatment alone. Off-label administration of cinacalcet HCl, a calcimimetic approved for the treatment of secondary hyperparathyroidism, together with the vitamin D analog dihydrotachysterol, however, proved successful in controlling parathormone (PAH), bone-specific alkaline phosphatase (BAP), serum calcium, and phosphate levels.