I used the Lantus insulin glargine pen and the U-100 syringes. I previously used U-40s with ProZinc. Did your vet specify which syringe you should use?
Yes. Use a U100 insulin syringe for a Lantus insulin pen. You don't use the pen needles. See this picture that I created years ago for the FDMB and is now on other web sites / forums: