JEFFREY GREENSTEIN, MD: I don't believe that at this point we can say that one drug is clearly superior to another. I think we have trends which suggest that there are benefits with regard to the adverse event profile. I think we have some data that is consistent with the fact that the development of neutralizing antibodies is harmful in the sense that therapeutic benefit is lost. So if one has to look at each of these drugs based on neutralizing antibodies, we're likely to see a greater number of patients lose benefit with Betaseron or Rebif, and in fact have a higher adverse event profile with both of them. We have a better side effect profile with Avonex, and we have a far, far reduced occurrence of antibodies with Avonex. So those factors tend to weigh in in deciding which drug to use in the long term.

WILLIAM STUART, MD: MS treatment is a long-term treatment. You want to pick a drug that you can use for an extended period of time. There isn't any such thing as treating MS for a year or two years; this is a 40- to 50-year disease. So in my own particular case, I look for the drug that is going to provoke the least amount of problem so that the patient's compliance in taking it long-term will be good and the drug has to have enough outcome effectiveness to warrant using. So I think it's very important, neutralizing antibodies are very important in determining which drug to use, particularly if there is any truth to the issue that presence of the antibodies of one drug may counteract the effectiveness of another.