I have never heard of that, but it does make sense to use it for something like that. I don't know how it would work because the hairs on the inside of your nose actually work to move dirt and debris out of your nose. But hey, it works so do it.

Since it's a topical treatment, I wouldn't worry about using too much antibiotics. It's not like it's clogging up his system and killing off his healthy bacteria like ingestible antibiotics. The only concern that I would have is that getting small colds are what strengthens your immunity to the bigger things, so unless it's really necessary to do it, it might be better to let him have the little colds because it's actually a good thing, if that makes sense.