I det samme studie blev der set en 25% stigning i AUC for theophyllin (markør for cytokrom P450 1A2 aktivitet), hvilket viser, at Pegasys er en moderat hæmmer af cytokrom P450 1A2 aktivitet.
In the same study, a 25% increase in the AUC of theophylline (marker of cytochrome P450 1A2 activity) was observed, demonstrating that Pegasys is an inhibitor of cytochrome P450 1A2 activity.