If you had known of the possible side-effects, were responsible for the child's care, and knew the condition of the child, would you have refused the treatment going in? I think not, nor would any rational person.
If I was told the possible side effects, my daughter was dehydrated, and they wanted to give her this drug, I would have asked all kinds of questions. The problem is too many emergency rooms or doctors do not give parents the information they need IMHO to make a decision.
She was given the drug and then sent home where she had the first seizure, rushed back to the hospital, suffered a second seizure and quit breathing, was stabilized and transferred to OU Medical Center.
At least if you knew the side effects, you would be on the lookout for any signicant change in your child.