I'll correct myself- if a patient is gone, it can't be a 'med error'. If your policy states a med/IV must be given within so many hours since the last dose, and that can't happen- always safe to get the order I mentioned. It also serves to document that you informed the MD that a patient on IVs was out of the building, if a surveyor makes an issue of a late or missed dose, etc.
I agree, never hold something without the MD being informed, especially antibiotics which need to be given on time, as scheduled. I know the patient being out of the building was not your fault, however.
I would give the med and call pharmacy to retime the antibiotic.