. ▁The ▁middle ▁res er voir ▁layer ▁holds ▁the ▁drug ▁and ▁is ▁tail ored ▁to ▁provide ▁the ▁specified ▁dos age . ▁The ▁final ▁inner ▁layer ▁consists ▁of ▁the ▁mu co ad hes ive , ▁allowing ▁the ▁patch ▁to ▁ad here ▁to ▁the ▁specified ▁m uc osa . ▁ ▁G els ▁As ▁a ▁liquid ▁or ▁sem is olid ▁dos age , ▁g els ▁are ▁typically ▁used ▁where ▁a ▁solid ▁form ▁would ▁affect ▁the ▁patient ’ s ▁comfort . ▁As ▁a ▁trade - off , ▁conventional ▁g els ▁have ▁poor ▁ret ention ▁rates . ▁This ▁results ▁in ▁un predict able ▁losses ▁of ▁the ▁drug , ▁as ▁the ▁non - sol id ▁dos age ▁is ▁unable ▁to ▁maintain ▁its ▁position ▁at ▁the ▁site ▁of ▁administration . ▁Mu co ad hes ives ▁increase ▁ret ention ▁by ▁dynamically ▁increasing ▁the ▁vis cos ity ▁of ▁the ▁gel ▁after ▁application . ▁This ▁allows ▁the ▁gel ▁to ▁effectively ▁admin ister ▁the ▁drug ▁at ▁the ▁local ▁site ▁while ▁maintain ing ▁the ▁comfort ▁of ▁the ▁patient . ▁ ▁Sol utions ▁These ▁dos age ▁forms ▁are ▁commonly ▁used ▁to ▁deliver ▁dru gs ▁to ▁the ▁eye ▁and ▁nas al ▁cav ity . ▁They ▁often ▁include ▁mu co ad hes ive ▁polym ers ▁to ▁improve ▁ret ention ▁on ▁dynamic ▁m uc os al ▁surfaces . ▁Some ▁advanced ▁eye ▁drop ▁form ulations ▁may ▁also ▁turn ▁from ▁a ▁liquid ▁to ▁a ▁gel ▁( so ▁called ▁in ▁situ ▁g elling ▁systems ) ▁upon ▁drug ▁administration . ▁For ▁example , ▁gel - form ing ▁solutions ▁containing ▁Pl ur on ics