Fenoterol  is an investigational drug in the United States that has been in use in Europe since 1970. It is the p-hydroxyphenyl derivative of metaproteronol,  and the combination of the resorcinol ring and the bulky p-hydroxyphenyl isopropyl group on the nitrogen gives fenoterol  significant β2-receptor selectivity. It has approximately half the affinity for the β2-receptor as compared to albuterol. The resorcinol ring is resistant to COMT metabolism, and the bulky nitrogen substituent greatly retards MOA metabolism as well giving fenoterol  a reasonable oral bioavailability with pharmacokinetics similar to albuterol (i.e., rapid onset and a 4- to 6-hour duration of action after oral inhalation).