What Causes Itchy Rashes On Withdrawal From Montair LC?

My mother is asthematic n she has been taking montair lc from a very long time. Earlier she took montair plus but doctor changed it. Now even if she skips the medicine for a day she gets rashes n scratching. N also it iz impossible for her to survive without it now. Please tell iz it harmful also n iz there any substitute or solution for it. To avoid these problems?