Not all powdered form inhalers contain lactose, nor do all forms of
Singulair. You need to check each one individually. The great thing about
the web is that you have access to most of the manufacturers' web sites,
which generally post the full information sheets of their medications.

You can ask your doctor to write for medications not containing lactose,
and can even ask her/him to specify that no substitutions be made. Also, if
the medication is not formulary for your coverage, you can ask your doctor
to write a letter supporting a request for exeption.

Hope that helps.

Mark