Acer Therapeutics & Relief Therapeutics Announce Update on US FDA Review of NDA

Acer Therapeutics Inc. and its collaboration partner, Relief Therapeutics recently announced the US FDA has issued a Complete Response Letter (CRL) regarding the New Drug Application (NDA) for ACER-001 (sodium phenylbutyrate) for oral suspension for the treatment of patients with urea cycle disorders (UCDs).

The CRL indicates that the FDA cannot approve the NDA in its current form. The CRL states: “[The FDA’s] field investigator could not complete inspection of [Acer’s third-party contract packaging manufacturer], because the facility was not ready for inspection. Satisfactory inspection is required before [the NDA] may be approved. Please notify us in writing when this facility is ready for inspection.”

The FDA did not cite any other approvability issues in the CRL pertaining to the NDA, nor request any additional clinical or pharmacokinetic studies be conducted prior to FDA approval. The FDA did provide one comment in the CRL (identified as “not an approvability issue”) requesting additional existing nonclinical information to be provided in the resubmission of the NDA.

Acer is actively collaborating with its third-party contract packaging manufacturer and cooperating with the FDA to address the FDA’s comments as soon as reasonably possible and currently intends to resubmit the updated NDA for ACER-001 (sodium phenylbutyrate) for oral suspension for the treatment of patients with UCDs in early-to-mid Q3 2022.

“While the outcome of the NDA review was not what we had hoped for, multiple rounds of labeling negotiations have already been conducted to date and we believe the recommendations raised by FDA can be appropriately addressed. We should be able to resubmit the NDA relatively quickly,” said Chris Schelling, CEO and Founder of Acer. “We remain committed to bringing a new treatment option to patients in the US with UCDs.”

ACER-001 (sodium phenylbutyrate) is being developed for the treatment of various inborn errors of metabolism, including UCDs and Maple Syrup Urine Disease (MSUD). ACER-001 is a nitrogen-binding agent in development for use as adjunctive therapy in the chronic management of patients with UCDs involving deficiencies of carbamylphosphate synthetase (CPS), ornithine transcarbamylase (OTC), or argininosuccinic acid synthetase (AS). ACER-001 is a polymer coated formulation that, when taken within 5 minutes, helps prevent the coating from dissolving. ACER-001 has been granted orphan drug designation by the FDA for MSUD. ACER-001 is an investigational product candidate which has not been approved by FDA, the European Medicines Agency (EMA), or any other regulatory authority. There can be no assurance that Acer will be able to meet its intended resubmission timeline for the NDA, that FDA inspection of the third-party contract packaging manufacturer facility will be satisfactory, that such inspection is the only impediment to FDA approval of a resubmitted NDA, that a resubmitted NDA will otherwise be approved by the FDA, or that ACER-001 will be approved for any indication.

Acer is a pharmaceutical company focused on the acquisition, development, and commercialization of therapies for serious rare and life-threatening diseases with significant unmet medical needs. Acer’s pipeline includes four investigational programs: ACER-001 (sodium phenylbutyrate) for treatment of various inborn errors of metabolism, including urea cycle disorders (UCDs) and Maple Syrup Urine Disease (MSUD); ACER-801 (osanetant) for treatment of induced Vasomotor Symptoms (iVMS); EDSIVO (celiprolol) for treatment of vascular Ehlers-Danlos syndrome (vEDS) in patients with a confirmed type III collagen (COL3A1) mutation; and ACER-2820 (emetine), a host-directed therapy against a variety of viruses, including cytomegalovirus, Zika, dengue, Ebola and COVID-19. For more information, visit

Relief focuses primarily on clinical-stage programs based on molecules with a history of clinical testing and use in human patients or a strong scientific rationale. Relief has a Collaboration and License Agreement with Acer Therapeutics for the worldwide development and commercialization of ACER-001 (sodium phenylbutyrate) for the treatment of various inborn errors of metabolism, including UCDs and Maple Syrup Urine Disease (MSUD). Relief also continues to study aviptadil for several possible lung-related conditions. Finally, Relief’s 2021 acquisitions of APR Applied Pharma Research SA and AdVita Lifescience GmbH brought to Relief a diverse pipeline of marketed and development-stage programs. For more information, visit