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# Reg Review Period for Ultragenyx’s Crysvita
- URL: https://www.fdaweb.com/reg-review-period-for-ultragenyxs-crysvita/
- Published: 2019-12-02T12:00:00.000Z
- Updated: 2026-09-14T15:54:55.000Z
- Author: David McFarland
- Tags: FDA Policy/General, #legacy-id-D5145614

*Federal Register* notice: FDA has determined for patent extension purposes the regulatory review period for Ultragenyx’s Crysvita (burosumab-twza), indicated for treating X-linked hypophosphatemia in adult and pediatric patients. The regulatory review period is 3,485 days, which includes 3,241 days that occurred during the testing phase and 244 days that occurred during the approval phase. To view the notice, click [here](https://s3.amazonaws.com/public-inspection.federalregister.gov/2019-25821.pdf?ref=fdaweb.com).