Administration of Pegasys 180 micrograms once weekly for 4 weeks in healthy male subjects did not show any effect on mephenytoin, dapsone, debrisoquine and tolbutamide pharmacokinetics profiles, suggesting that Pegasys has no effect on in vivo metabolic activity of cytochrome P450 3A4, 2C9, 2C19 and 2D6 isozymes.