Now i'm not a doctor obviously however i have a good amount of knowledge with biochem and physio. Lasix being a diuretic poses a problem here as creatine usage necessitates proper hydration. I'd say no, for two reasons: one being that i don't see it to be that safe, two being that creatine doesn't provide amazing gains to warrant the risk. Creatine can help get some extra reps out but otherwise it's not adding muscle directly.