Description: Fosdagrocorat (formerly known as PF-04171327) is a phosphate ester prodrug of PF-00251802 (dagrocorat), a selective high-affinity partial agonist of the glucocorticoid receptor, which is further metabolized to PF-04015475. Dagrocorat (also known as PF-00251802) is a novel and potent dissociated glucocorticoid receptor agonist with the potential usefulness as an anti-inflammatory agent. The dissociated agonists of the glucocorticoid receptor are a novel class of agents in clinical development for rheumatoid arthritis. PF-00251802 is a reversible inhibitor of several CYPs, but modeling has suggested no clinically relevant interaction. PF-00251802 and PF-04015475 are time-dependent inhibitors and inducers of CYP3A in vitro; PF-00251802 is also a time-dependent inhibitor of CYP2D6. Model-based prediction suggested the potential for weak inhibition of CYP3A in vivo. A clinical DDI study was conducted with midazolam, a sensitive CYP3A substrate. A phase 1 open-label, multiple-dose study evaluated the effect of PF-04171327 on midazolam pharmacokinetics and safety in 12 healthy volunteers. Administration of midazolam alone or concomitantly with PF-04171327 resulted in equivalent pharmacokinetic profiles (AUCinf , 21.17 vs 20.28 ng·h/mL, respectively), indicating that PF-04171327 had no net effect on CYP3A activity in vivo. These findings support the further development of PF-00251802 and PF-04171327 as potential treatments for patients with rheumatoid arthritis (NCT00987038).