The Food and Drug Administration (FDA) has approved Olpruva (sodium phenylbutyrate) as an oral suspension for the treatment of patients with urea cycle disorders (UCDs).

Olpruva, a nitrogen-binding agent, is indicated as adjunctive therapy to standard of care, including dietary management, for the chronic management of adult and pediatric patients weighing 20kg or greater and with a body surface area of 1.2m2 or greater, with UCDs involving deficiencies of carbamylphosphate synthetase, ornithine transcarbamylase, or argininosuccinic acid synthetase.

The approval was based on data from 2 bioequivalence trials, which showed similar relative bioavailability for both phenylbutyrate and phenylacetate when compared with Buphenyl (sodium phenylbutyrate). The application, which was submitted through the FDA’s 505(b)(2) regulatory pathway, contained preclinical and clinical safety and efficacy data from the reference listed drug, Buphenyl. 

The most common adverse reactions reported with sodium phenylbutyrate are menstrual dysfunction, decreased appetite, body odor and bad taste or taste aversion.

Olpruva is supplied in dosage strengths of 2g, 3g, 4g, 5g, 6g, and 6.67g of sodium phenylbutyrate as pellets in packets for reconstitution. Each dose is packaged in a dosage envelope containing 1 or 2 packets of sodium phenylbutyrate and a suspending agent packet. A 30-day supply is provided in a kit containing 90 dosage envelopes.

“The FDA’s approval of Olpruva, an innovative formulation of sodium phenylbutyrate packaged for the first time in single-dose envelopes, marks the culmination of our ongoing dedication to develop new and differentiated treatment options for those affected by rare diseases,” said Chris Schelling, CEO and founder of Acer. “Patients who are living with UCDs now have an alternative treatment option with Olpruva, to address some of the challenges they may have with existing therapy.”


  1. Acer Therapeutics and Relief Therapeutics announce US FDA approval of Olpruva for patients with urea cycle disorders. News release. Acer Therapeutics and Relief Therapeutics. December 27, 2022. Accessed December 29, 2022.
  2. Olpruva. Package insert. Acer Therapeutics; 2022. Accessed February 17, 2022.