I also use pre-filled Lovenox syringes. They come in whatever doseage you need, I use 40 mL once per day. Heparin is only a 12 hour shot, so you'll probably need to inject twice a day. If possible, see if you can be on Lovenox instead. It's the same medicine, except Lovenox stays in your system for 24 hours, so depending on your situation you may only need to inject once like me. I would definitely look into it if your insurance covers it. It's much more expensive than heparin so make sure your insurance covers it.