Doping

But, that's 400ug, not the 2000 or whatever Froome has failed the test for.

It's 400μg at once, which is double the usual dose but still within the WADA limit if you do that every six hours. The problem with that regime would be that at some arbitrary point between doses, your elimination rate is likely to go over 1000ng/ml. The 1000ng/ml threshold seems to based on an average athlete under average conditions taking 200μg every 3 hours, with a bit of headroom. Froome could legally have taken 800μg all at once during the stage, as long as that was his first dose that day, and if the dopage happened to coincide with his peak elimination rate, it's easy to see how a 2000ng/ml reading could be achieved. It would be an odd thing for an athlete or an experienced asthmatic to do, except in case of emergency, but if he goes into a test cell and simulates the timing, workload and atmospheric conditions of the day and hits the 200μg inhaler 4 times in a row, I bet he can piss out 2000ng/ml and make this little problem go away.