The main thing is that vials are only tested for safety through 28 days. It's not a date that means that the drug is ineffective after four weeks, but it means that we don't know exactly what will happen after that. It is possible that the vial may become contaminated, and I would not want to risk a patient injecting something we don't know is safe. In this case I do the same thing that your pharmacy does and dispense 10 1mL vials rather than 1 10mL. It generally saves people money to use just the required dose than to toss out the remainder after the 28 days. When you refill next, try calling your pharmacy and asking them to check the price on a 10mL vial and a month's worth of 1mL. Depending on if/how your insurance covers them, the price may be different, but in general the copays are the same for the same volume regardless of the size of vial being dispensed. If you're paying out of pocket, it may vary.