To reduce this class of errors, perhaps RFID tags could be used? If the medication is prepared in a low-distraction area and tagged there, then the person administering the medicine would scan the tag to make sure it's correct before going through with it. The person tagging the medication could still make a mistake, but it would be harder for everyone else, and perhaps during the tagging process some kind of automatic flagging could be employed if the medication doesn't seem to match the patient's problems.
This is already being done in a small number of hospitals in the USA and other parts of the world. The problem is mainly the resources (money and time) needed to repackage all the drugs to their own unit doses fast enough. Most of the time a barcode / QR code / equivalent 2D printed codes suffices and is much cheaper (and more flexible) than RFID tags.
However, you won't believe the kind of things that go wrong with this approach either. It's basically operating a manufacturing plant inside a pharmacy / hospital, but without presence of anyone titled "engineer".
In an ideal world, the drug authority (FDA) would require all manufacturers to print proper barcodes in all unit doses at the time of manufacture.
