Pharmacokinetics and elucidation of the rates and routes of N-glucuronidation of PF-592379, an oral dopamine 3 agonist in rat, dog, and human

PF-592379 is a potent, selective agonist of the dopamine 3 receptor, for the treatment of male erectile dysfunction and female sexual dysfunction. In vivo, PF-592379 has low-moderate clearance relative to liver blood flow of 6.3 and 8.5 ml/min/kg in dog and 44.8 and 58.2 ml/min/kg in rat. It has high permeability in Caco-2 cells and was completely absorbed in rat and dog pharmacokinetic studies with an oral bioavailability of 28% in both rats and 61 and 87% in the dogs. These data are consistent with the physicochemical properties of PF-592379, which indicate complete absorption by the transcellular route. Elimination of PF-592379 was predominantly metabolic in nature. In vitro routes of metabolism studies indicate that metabolism in the rat is a combination of P450 mechanisms and N-glucuronidation, whereas in dog and human, N-glucuronidation is the major route. NMR analysis indicates that N-glucuronidation is non-quaternary in nature and occurs on both the pyridyl amine and ring nitrogen. Rates of clearance via N-glucuronidation were predicted to be low in humans compared with acyl or phenolic glucuronidation. PF-592379 was predicted to have complete absorption from the gastrointestinal tract and an oral bioavailability of > 60% in the clinic. Clinical data verified that PF-592379 is a low clearance compound in human, with a mean oral clearance of 6.5 ml/min/kg following a 200 mg oral dose. PF-592379 has ideal pharmacokinetic properties for an oral D3 agonist, intended for on demand dosing.