Single dose vial meds

if a patient is ordered 25mcg of fentanyl times 3 doses till pain free q 10 minutes... can you draw up the whole vial of fentanyl 100mcg and then hold the rest and give the followup administration from that same syringe to the SAME patient as long as the med syringe is sterile capped between each dose?? i cant find squat that says you cant or that you can... it just states cant be done on multiple patients and a single dose vial should not be reentered multiple times for the same patient.
I dont work in an OR but dont they give sedation from a syringe and titrate the dose?? do they never disconnect??