Whilst reports exist of increases in the INR of people taking warfarin and oseltamivir, the mechanism for a possible interaction has not been proposed.  Whilst a specific interaction between warfarin and oseltamivir (or zanamivir) cannot be ruled out, it may be that the fever associated with swine flu is a more likely cause of these cases of raised INRs in people on warfarin. 

The MHRA have set up a specific section of their website (http://swineflu.mhra.gov.uk/) for the public and professionals to report suspected side effects to particular medications administered during this time period to manage influenza.