My local LFS recommended PolypLab Medic. It won't eradicate ick, but it's suppose to suppress them in the free floating stage. I've been dosing it for 10 days, and I haven't lost any fish (fingers crossed). 2nd round of ick (after they initial fall off and reproduce) was significantly less (only a few fish broke out and nowhere near as bad). .
I don't know this product but I'll play devil's advocate and mention that the progression you describe is often the case for ich/crypto, even without any medication.
For ich/crypto management, going that route successfully imo involves uncrowded nonstressful conditions, clean water, a strong UV sterilizer, and no new additions for a long time.