My Kid Is 4.5 Year Girl.she Develops Upper Resp Tract

My kid is 4.5 year girl.she develops upper resp tract infection frequently. Response to antibiotics also slow and disease severity more. No effect of other antiallergics except montelucast her symptoms remains suppressed but as soon as she stops taking it after 3-4 days severe attack of infection.kindly to how long can I give mytikato her and will it affe t her in llong term mean her growth.than.