My daughter, Hayley, who is only 4 has been on IV tobramycin at least 6 times if not more. OUr doctor checks the level after every third dose. They draw right before the does is given and then a half hour after the does is given. The dosage can be tricky until you get it just right. When it is not high enough, you are not getting enough to fight off the PA and when the level is too high you risk hearing damage. I would defintely call and have them check the levels ASAP!