Knight was treated with ampho-b back in 2002 in conjunction with Itraconazole. Back then it was said that the two drugs together had a synergistic effect. When my Vet conferred with some successful blasto Vets, the opinion was that using Ampho-b until the dogs fever broke was the preferred treatment. It's my opinion, from my vet, that renal functions should be monitored all the while ampho-b is being used.
Originally, my vet was only going to proscribe Intraconazole orally to treat the blasto. I dug around and found some successful vets in Wisconsin using Ampho-b in conjunction with an "-azole". I referred my vet to a vet in Tomahawk that was touting the combined therapy. My vet agreed and we put Knight on every other day ampho-b and alternating days renal blood work up.
Additionally, a few years ago a coworker caught blasto in the UP of Michigan. They used Ampho-B and Itraconazole on him at that time as well. Both my dog, Knight, and my Coworker survived.
I do know that ampho-B is called amphoterrible for a good reason. It is harsh. During Knight's treatment, a catheter pulled part way out and a bunch of ampho-b laden saline solution filled up the space under his skin on this foreleg, at the site of the IV cath. I caused an ugly ulcer about the size of a dime.
Current wisdom might have changed, but if your vet is using Ampho-b as a stop gap measure and using it in conjunction with one of the "-azoles" AND monitoring renal functions often, then it's been known to work and is even used in humans. (at least up to a couple years ago).
It's always been my opinion that ampho-b isn't a poor choice because it's ineffective, but rather it's harsh. At some point, you have to weigh the pro's and con's of using a harsh drug. It might be harsh, but then it might be the last trick up your Vet's sleeve. I'm here to tell ya, that used wisely, it can save lives. Of course that depends on the situation, and one thing I've learned, every situation is different when it comes to blasto.
FWIW, Itraconazole is less harsh, but it stress's the liver, where it's metabolized. High dose Itra over a long time can cause liver issues. Read the packing insert and contraindications that come with an Itra script. None of these drugs are without side effects and they all have their down sides.