Replies to post #75028 on Biotech Values

[DewDiligence]

BIIB ELN re Tysabri PML rate:

Sandrock's quote: "…since Tysabri's reintroduction the PML rate is about 1 in 4,000 over 12 months of exposure"; Dew's quote: “1 in 4,000 during the initial 12 months of treatment”

You’re correct—my use of the word initial is wrong; Sandrock is saying that the rate of PML is now approximately 0.25 cases per thousand patient years, but he is not making any assertion whatsoever about how many PML’s occur in the first year of treatment.

Now let’s get to the crux of my prior post. My point in #msg-36568162 is that it was misleading for BIIB to compare a PML rate over 12 months to a PML rate over 28 months, which is the median duration of treatment for MS patients in Tysabri’s FDA label. To make an apples-to-apples comparison, we should express both PML rates in terms of cases per thousand patient years; these figures are 0.25 cases for the newly reported PML rate by BIIB and 0.4 cases for the PML rate in the FDA label (making the simplifying assumption that the median and mean in the FDA label are roughly the same).

In other words, the PML rate reported by BIIB on yesterday’s webcast is 38% less than the PML rate in the FDA label—not 75% less, as BIIB’s comments during the webcast may have led some people to believe.