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I'm sorry to hear about your son's situation. Legally speaking, yes, the nurse can do this. The nurse has discretion as to medication distribution given the condition of the patient, etc... Now I'm certainly not saying that the nurse was right in doing this. But there was no law that was broken by the nurse withholding the medications.
Now her actions could have been unethical, unprofessional, and even potentially dangerous, and could be the basis for a complaint (http://www.op.nysed.gov/opd/complain.htm for more information about filing a professional misconduct complaint) but as far as any "private cause of action" (a lawsuit) it would be very difficult to do so, if there was no quantifiable damage resulting from a clear abuse of discretion / negligence. Again, what was done is not illegal, and at best it would be the basis of a complaint through the link above.
I know this is probably not what you wanted to hear, but it is the law. I hope that clears things up anyway. If you have any other questions, please let me know. If not, and you have not yet, please rate my answer AND press the "submit" button, if applicable. Please note that I don't get any credit for the time and effort that I spent on this answer unless and until you rate it positively (good or better). Thank you, ***** ***** luck to you!