After a personnal experance at almost losing a pet DO NOT buy an over the counter product. I don't care how much it costs losing a pet or the vet bill to save them justifies the cost. $500.00 to save our winky . It would have been only $40.00 to have both cats done.
My vet says Bio Spot is one of the worst 1 out of 500 animals have a reaction to it . in cats that means death as there is no antadote. Luckly I had not used it, but the seazues were terrible to witness and he was in an intensive care for 3 days. I was lucky they are a caring and compassinate couple of vets.
I know how you care for your animals . just call the vet he may be able to do it for just the price of the meds. Never hurts to try.