So in a week I'm going back so the vet can check Charlies ear mites and also the doc said I could Charlies heartworm medicine and I'm pretty sure I should buy from 1800 petmeds to save some money. I've already bought one month (but don't remember the name). What if 1800 petmeds sodesnt have what she gives and will it be okay to switch the brand and if so what brand is safe for Yorkies?