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Post# of 19309
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DewDiligence

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DewDiligence

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Re: exwannabe post# 6847

Wednesday, 01/09/2008 6:37:05 PM

Wednesday, January 09, 2008 6:37:05 PM

Post# of 19309
Re: US ATryn trial design

>But how else "dew" you get the delta?<

By negotiation!

>If the NI margin was such that a placebo has a good chance of passing, you have a real problem.<

That’s true; however, the NI delta is typically set much smaller than the presumed differential between the comparator arm and placebo, so this problem does not come into play in practice.

>Let's take this trial as an example. If sDVT occurs at a rate of 30% w/o AT, then it's obvious that a NI delta of 10-15% is "reasonable". BUT if sDVT only occurs at a rate of 5%, then a NI delta over 3-4% is absurd.<

Agreed. Given that 30% is the approximate rate of sDVT for this patient pool on placebo, I would expect the negotiated NI delta for this trial to be in the 8-15% range. (If GTC had forceful negotiators, the delta is probably closer to 15%; if not, it’s probably closer to 8%.)

Given the number of patients in this trial and the fact that the arms are roughly 1:1 in size, an 8-15% range is approximately 3-6 patients. In other words, in the worst case according to my numbers, the ATryn arm needs to have no more than 2 additional cases of symptomatic DVT than the control arm.

However, 14 of the ATryn-arm patients—the ones from the European trial—are already known to not have sDVT. Hence, in order for the trial to fail on efficacy, the number of sDVT cases in the 17 “new” ATryn-arm patients would have to exceed the total number of sDVT control-arm cases by 3 or more. Possible but not likely, IMO.

“The efficient-market hypothesis may be
the foremost piece of B.S. ever promulgated
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