Tafluprost (free acid)-d4 contains four deuterium atoms at the 3′, 3′, 4′, and 4′ positions. It is intended for use as an internal standard for the quantification of tafluprost (free acid) (Item No. 10005439) by GC- or LC-mass spectrometry. A number of 17-phenyl trinor prostaglandin F2α (Item No. 16810) derivatives have been approved for the treatment of glaucoma.1,2,3,4 Of these, the ones wherein the 13,14-double bond has been hydrogenated retain relatively good potency, but show a significantly reduced incidence of local irritant side effects.5 Alternatively, it was recently reported that analogs incorporating a 15-deoxy-15,15-difluoro modification also had a favorable ophthalmic activity profile.6WARNING This product is not for human or veterinary use.