Hi
@RuWo,
Fiasp is is NovoRapid with added nicotinamide/B3 to make it absorb faster - work beautifully for some, and not for others.
My experience was (used it off and on for 6 months or so) it worked amazingly for something like 6 weeks, then I started to get issues.
As
@Nicola M says with Lyumjev (similar insulin action profiles), don't pre-bolus so bolus from your pump when the food is in front of you - and watch out for high carb/fat meals (pizza) as the insulin will kick in before all the carbs are digested.
When going high (14 or so), lots of people (me included) found it took a lot more insulin to make it drop my BG - only way I could make it work was to inject Fiasp into my leg rather than bolus using the pump - then it worked as expected (though still needing about 1/3 more than when in normal range).
My observation was I had resistance at the sites I was using from my cannula sites - moving them to new bits (sides etc) where I didn't normally put the cannula helped a lot and made the insulin more responsive.
In the end I switched to Lyumjev - and had similar issues till (I worked out about site rotation - a long path to get there). I've found Lyumjev to work better for me (Lyumjev is Humalog with a vasal dilator - Treprostinil - added to speed up absorption)
You might be fine with Fiasp if you can avoid pre-bolus and do good site rotation.
Stinging - yes, this goes off after time (took about 3 months, had a break from it and returned and no stinging), your body does get used to it.
Lyumjev was the same - but my body got used to the Treprostinil after a good while (I tried mixing insulins, which isn't recommended, and that seemed to lessen the pain and made the insulin absorb better - but eventually I ended up with resistance again (due to site rotation I think)