Question:

Everyone knows about amphotericin B and the potential side effects. But what happened to amphotericin A?

Answer:

Amphotericin A didn’t have useful antifungal activity, so during the original manufacturing process of amphotericin B the goal was solely to reduce the amount of amphotericin A below 15% (much lower now).  Toxicity was not improved with reductions in amphotericin A so its unlikely to significant contribute to toxicity either.