You're going to need a complete list of html tags you want to remove then (i, em, b, what else?) since you're going to have to search specifically for the tags to remove.
One way of doing this is: \b(i|em|b)(\w*)\/(i|em|b)\b
(and as you've seen before with Obj-c, likely some double \ escaping)
In action: http://regex101.com/r/qL3cU9
Input:
- iword/i
- emword/em
- bword/b
- ibword/ib
- notgoing/tomatch this
Substitution result:
- word
- word
- word
- ibword/ib
- notgoing/tomatch this