Jack, as both the Twisthaler and the DIskus are "dry powder inhalers",
their ability to perform properly reduces as moisture gets into the
very fine powder within.  The Twisthaler has a big reservoir of drug,
which is measured out bit-by-bit as you prime it before each
inhalation.  The DIskus is a bit different, because each of its doses
are individually-wrapped on a long foil strip - each dose has its own
"foil pouch", by comparison to the Twisthaler.  It is therefore likely
to be more resistant to moisture over time, which allows the
manufacturer to allow people to keep it for longer (once the foil pouch
protecting the reservoir devices such as Twisthaler or Turbohaler is
opened, moisture will be absorbed by the dry powder in the "hopper"
inside these devices).

Schering are likely required to state a time limit for normal use - the
Twisthaler may still be able to perform properly after 45 days, if it
is kept away from moisture as much as possible.

Me ? - I keep my spare inhaler inside a self-seal poly-bag, and after
I've used it, I wipe the mouthpiece with a cloth to make remove as much
moisture as possible before I put it back.  It stays well clear of the
bathroom, too.

Kind regards, Jon Bell (Canday Medical Ltd)

[please ignore email address - it is incorrect]