Fenspiride-d 5 is the deuterium labeled Fenspiride. Fenspiride, an orally active non-steroidal antiinflammatory agent, is an antagonist of H1-histamine receptor. Fenspiride inhibites phosphodiesterase 3 ( PDE3 ), phosphodiesterase 4 ( PDE4 ) and phosphodiesterase 5 ( PDE5 ) activities with -log IC50 values of 3.44, 4.16 and approximately 3.8, respectively. Fenspiride can be used for the research of respiratory diseases.