[exim] Regex

Hello,

I have a question about regex:

regex = (i?)viagra : (i?)cialis

This reliably triggers "viagra" and "cialis" in any upper-/lowercase
combination. But "cialis" is embedded in words like spe"cialis"t (not
very seldom in regular mails :-)

So i tried something like

(?i)\scialis\s

Pcretest says ok and matches caseless "cialis" surrounded by whitespace.
In the exim regex line this term doesn't matches. What I'm doing wrong?
Should I enclose the term with a pair of "\N"?

TIA,
Peter