The night before last I was transcribing orders in an AL facility. I wrote an order for an antibiotic in the wrong patient's MAR. The med tech came for it and the wrong patient received the medication from the back-up supply. It was not caught until a second nurse double checked the orders 12 hours later. I was only made aware of the error 24 hours later by the aide talking about a patient receiving the wrong medication. My heart immediately sank. I am devastated that I could have made a lethal error. Thankfully, the patient does not have a Sulfa allergy and has had no ill effects.I am so relieved the patient was fine. I am saddened that the nurse who noticed the error is the one I took over for. Is it common not to inform someone of a such a severe error? Was she afraid of my reaction? Why would anything like that be her concern when I needed to be informed for patient safety? Had the aide not mention anything to me, I very well may not have been informed until I received the transcription error several weeks from now.I am beside myself and I cannot comprehend how I let this happen.