My Daughter Is Suffering From Severe Sneezing Fo Last 6-7

My daughter is suffering from severe sneezing fo last 6-7 years, if she takes antihistamine she is alright , but if she miss it one day also she start sneezing. I consulted ENT the said this is due to prepare allergy and at present he prescribed Romilast 10mg . I just want to know whether it has any side effects and is there any permenent relief for that . Her age is now17 years.please suggest.