Not sure myself. Planning to follow along with how this turns out.
I used to wipe the cartridge on my injector pen with a folded isopropyl pad before attaching a new needle. It was awkward and I never felt sure it was clean enough. Then I tried some alcohol swabsticks instead and they reach the recessed rubber stopper much better because you just bend them to release the liquid. They turned out to contain ethanol rather than isopropyl, but online information says the two work equally well. I have only ever seen isopropyl in medical environments and wonder what others think.