Dec 23 (Reuters) - The U.S. Food and Drug Administration (FDA) has approved Acer Therapeutics Inc's drug for treating patients with a type of genetic disorder called urea cycle disorders (UCDs), according to the health regulator's website.

The approval letter, issued on Thursday, said the drug, sodium phenylbutyrate, could be used as an adjunctive therapy to the standard of care for patients with UCDs with certain deficiencies.

UCD is a genetic condition that causes toxic ammonia to build up in the blood due to the deficiency of certain enzymes.

The company resubmitted its marketing application for the drug in July after it got the so-called complete response letter from FDA in June.

The company did not immediately respond to a Reuters request for comment about the drug's pricing and availability. (Reporting by Raghav Mahobe in Bengaluru; Editing by Anil D'Silva)