17-phenyl trinor Prostaglandin F2a ethyl amide (17-phenyl trinor PGF2a ethyl amide) is an F-series PG analog which has been approved for use as an ocular hypotensive drug.{8941} 5-trans-17-phenyl trinor PGF2a ethyl amide is an isomer of 17-phenyl trinor PGF2a ethyl amide wherein the double bond between carbons 5 and 6 has been changed from cis (Z) to trans (E). The trans isomer of 17-phenyl trinor PGF2a ethyl amide occurs as an impurity in commercial preparations of the bulk drug product. The present compound was prepared primarily as an analytical standard for detection and quantitation of this impurity. From what can be inferred from the study of other trans isomers of F-type PGs, the biological activity of this isomer is likely to be similar to that of the cis isomer. However, there are no specific published reports on the biological activity of 5-trans-17-phenyl trinor PGF2a ethyl amide.