Drug Interaction Report

MONITOR: Concomitant use of glycerol phenylbutyrate with medicines known to inhibit pancreatic lipases may theoretically lead to reduced intestinal absorption of its active moiety phenylbutyrate, and hence reduced control of plasma ammonia levels. After oral ingestion, pancreatic lipases hydrolyse glycerol phenylbutyrate in the small intestine to glycerol and phenylbutyrate, allowing the absorption of phenylbutyrate and its subsequent conversion to the active metabolite, phenylacetic acid, by beta-oxidation. Clinical data are not available.

MANAGEMENT: Caution and close monitoring of ammonia levels is recommended if glycerol phenylbutyrate is to be administered with a gastrointestinal lipase inhibitor such as orlistat. The dose of glycerol phenylbutyrate should be adjusted as necessary per local guidelines.