My Guinea PIg had mange and gave it to my bunny

[Lovely Birds]

Ok so I bought a guinea pig with out knowing it had the start of mange so I took it to the vet and he was giving me ivermectin it worked but I guess I stopped giving it to her to soon because she passed it to my rabbit that is in a cage right next to hers. He is going out of town for two weeks and said go buy some ivermectin but I don't know what brand to get and what kind to get. It was a injection kind I think, but he just had me put it on her skin or her back. Does anyone know what I should get I don't want to wait two weeks before treating it.