I have been using 40 iu vials (using 6mm BD syringes) for insulin for the last one month but I want to shift to insulin pen since it has 4mm needle size ,but the pen has cartridges of 100iu , how to convert the 40 iu doses to 100 iu ? Is 100iu cartridges more powerful than 40 iu vials For instance I take 28 units of insulin from the 40 iu vial how much should I take from the 100iu ,that would be equivalent