The fast is broken by what nourishes the body in the manner of food and drink (cf. Quran 2:187), so scholars such as Ibn Baz and the Standing Committee ruled that a nutritional IV drip breaks the fast because it takes the place of food and drink. Ordinary injections that only carry medicine (intramuscular or into a vein) do not break the fast, since they are not eating or drinking and do not nourish. Regarding the asthma inhaler, the strong contemporary view (Ibn Baz, Ibn Uthaymin) is that it does not break the fast, as the puff is a gas that disperses and does not reach the stomach as food. When in genuine doubt, the safest course is to schedule non-urgent treatment at night.
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.