long story short they are not equivilant...of course something is better than nothing. I do have an inhaler that I use when I can not get to my neb. There are several issues here though..the main one is that inhalers effectiveness are limited depending on the user and your user is not even 5 months old.
Just food for thought, remember Xopenex inhaler is 45mcg, Xopenex neb solution dosage for kids is normally .31Mg or .63Mg, I realize that the dosages can not be an apples to apples comparison as there are variances with inspiratory to expiratory ratio from patient to patient (especially if your young one is crying). But with inhalers it is all or nothing, with nebs you have 10-15 minutes to get your meds.
1 last thing..you realize Xopenex is really only approved to be used in kids over 6? Why did they choose it over albuterol? Not that it matters really, I have given Xopenex to plenty of kids and think it is perfectly safe but I always wonder why doctors choose the med that cost 2 dollars a dose over the one that cost 6 cents a dose?
hope this helps...have a nice day