>Good companies are always searching for ways to cannibalize their sales!<
Normally I'd agree with that. There are plenty of instances where--at least in a portfolio sense--multiple drugs from a single company in a single indication have led to an overall expansion in sales. It's never 1+1=2; more like 1+1=1.2. (Which, by the way, sucks for reps if they only carry one of the drugs). Companies with multiple hypertension products in their portfolio are good examples of this.
But MS differs from hypertension. The market isn't expanding, and there's no way to expand it by increasing awareness. Although I'm sure there's some wiggle room for expanding profits by moving more expensive newer drugs to earlier-stage patients and shifting older, less efficacious and/or less well tolerated agents up the treatment ladder to more advanced patients, the MS market is more or less fixed in terms of patient population.