HealthDay News — The FDA has approved glycerol phenylbutyrate (Ravicti, Hyperion Therapeutics) to treat certain urea cycle disorders (UCDs) in patients aged 2 years and older.

UCD is a rare inherited condition that involves a lack of enzymes that help the body remove ammonia from the blood. The body typically produces nitrogen as a waste product during protein metabolism. Nitrogen is normally converted to urea and excreted, but in people with UCDs, nitrogen accumulates as ammonia, and can lead to coma, brain damage or death, the FDA said in a press release.

Glycerol phenylbutyrate aids in removing accumulated ammonia, and is indicated for people with UCDs whose disorder cannot be managed with a protein-restricted diet or amino acid supplements alone. The liquid formulation is designed as an adjunct therapy to be taken three times daily with meals.

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“Ravicti provides another treatment for chronic management of urea cycle disorders, a group of life-threatening conditions,” said Donna Griebel, MD, of the FDA’s Center for Drug Evaluation and Research. The drug was reviewed under the agency’s fast track program and had been granted orphan drug status.

The approval was based on clinical trial results in 44 adults who had been receiving sodium phenylbutyrate (Buphenyl) for UCD. Patients were randomly assigned to continue taking the older drug or to receive glycerol phenylbutyrate for two weeks. Participants were then crossed over to the other treatment for two additional weeks.

Glycerol phenylbutyrate was just as effective as sodium phenylbutyrate in lowering levels of ammonia in the blood, the researchers found. The most common side effects were diarrhea, flatulence and headache.

“The approval of this new therapeutic option demonstrates FDA’s commitment to providing treatments for patients suffering from rare diseases,” Griebel said.

The FDA will require drug-maker Hyperion Therapeutics to conduct additional post-marketing studies to assess safety, ammonia control, drug interactions and more. Glycerol phenylbutyrate will be available in 1.1g/mL liquid in 25mL multi-use glass vials. It is expected to be available by the end of April 2013.

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