You should talk to an experienced family law attorney in your area.
Whether something is abuse or neglect only matters if child protective services agencies or the police are involved. If you are the custodial parent and what you want is to make sure the child gets necessary medication, you may need to file a contempt action against the visiting parent.
It may or may not be neglect depending on how serious the medical condition is. You should however document the situation and bring it to the Court's attention since the Court thought the medication important enough to order the parent to administer it.