First step is emphasizing to the young nurse that in a just culture, this error (though potentially fatal!) does not constitute grounds for dismissal nor does it define their nursing ability. Nurses make mistakes unfortunately and the most important aspect of these errors is honesty so that the patients have positive outcomes. The mistake was negligent but, understandable and this needs to be communicated as to not discourage future reporting.
Second, emphasize fundamental nursing principles. When busy, stressed, overwhelmed, etc., the likelihood of committing a medication error is amplified. So, go back to basics. Check the five rights (right patient, med, dose, route, and time) on the order, during preparation, and before administration. If vials look alike, checking for the correct medication at least three different times can prevent these errors.
Tried to stay within the parameters but instead did two short paragraphs of 6 lines.