NICDR CROMS: Gafni T-D-0030: Cinacalcet

Open-label Dose-titration Study of the Tolerability and Efficacy of Cinacalcet to Treat Fibroblast Growth Factor 23 (FGF23)-mediated Hypophosphatemia

This study is an open-label, dose-titration study of once-daily dosing of cinacalcet, with up to 4 escalating doses given at approximately 3 week intervals.  The primary objective of this protocol is to evaluate the tolerability of cinacalcet in individuals with fibroblast growth factor 23 (FGF23)-mediated hypophosphatemia, using an open-label, dose-titration study of once-daily dosing.  After an initial standard of care optimization period of 2-9 weeks, subjects will proceed to the cinacalcet dose-titration period.  Subjects who experience extended toxicity or study drug related serious adverse events or other related, intolerable adverse events will be down titrated to a lower dose of study medication.   After subjects have achieved their own maximum tolerated dose (MTD) and completed the once-daily dosing phase, they will continue the study medication for approximately 3 additional weeks with twice-daily dosing at their MTD.  At the end of the cinacalcet treatment phase of the study, cinacalcet will be discontinued and standard of care (SOC) medications will be adjusted/restarted on an individualized basis.  Subjects will continue in this final SOC safety follow-up period for up to 4 weeks until their SOC medications have been re-equilibrated.