Don't worry - there is one! The best treatment for asthma in cats is actually inhaled steroids (Flovent or Flixotide) and for most cats, inhaled steroids do not seem to increase blood sugar the way steroid pills and shots do. I suggest that your dad ask the vet about possibly changing Macho over to inhaled steroids to see how he does. Some cats need both inhaled and oral steroids to control their asthma but many (including Callie) do not need pills/shots at all. It is really important to treat asthma so as Elise said, if Macho does end up needing steroid pills, you can always adjust Macho's insulin as needed.
Some general info about Flovent/ Flixotide: It is a low-dose corticosteroid that works directly on the inflammation in the airway and is designed so very little enters the system to cause the systemic side effects that oral or injected corticosteroids cause with long-term use. It takes about 14 days to build in the system and is administered twice a day, 12 hours apart.
I was very surprised at how quickly Callie took to her inhaled meds ... it just took a bit of patience (and a bunch of treats!) to slowly get her used to the Aerokat, which is the device that is used to give the cats the inhaled medication. (Chewy link for Aerokat:
https://www.chewy.com/trudell-medical-international-aerokat/dp/175949 You can also buy it on Amazon, VetrxDirect etc.)
Flovent is very expensive in the US so a lot of people buy it online from Canadian or New Zealand pharmacies. We have been buying Callie's inhalers from InHouse Pharmacy for years and they have been great. (Link to Flixotide at InHouse
https://www.inhousepharmacy.vu/p-399-flixotide-fluticasone-cfc-free-250mcg-inhaler.aspx)
Here are a couple of videos showing how to train a cat to use the Aerokat:
Let me know if you or your dad have any questions or want any other info. Callie was diagnosed with asthma about four years ago and I'm happy to share what we've learned along the way.