Are you sure they have ear mites? Dandruff is normally associated with fur mites. Do they have crusts in their ears? Black “specks” way down in the ear would be more early stages. Your vet should be able to properly prescribe something, even if they are doubtful that it’s ear mites. With topical treatments, there’s no harm done if it turns out not to be mites.

We would need to know more information to help you with topical ivermectin dosage. What concentration is it? Was this something you purchased yourself or did the vet give it to you?

PSA – Do not use any products containing fipronil on your rabbit. Although effective against parasites, fipronil is toxic to rabbits and should be avoided.

Hmm… that isn’t very helpful because it doesn’t say how much ivermectin is actually in it. Assuming it is meant for horses, the concentration is probably high. You do not want to risk overdose. Would your vet be able to help you out with figuring out the correct dosage? Maybe they are familiar with the concentration of that particular formula. What about Revolution? You could ask your vet’s office for the kitten formula. That would be a lot easier to figure out the correct dosage.

Side note: Are you sure they aren’t just molting? My bunny will scratch his ears when he is molting because loose bits of fur will get in there and tickle his ears.

Cleaning the environment is an important component of ear mites treatment: https://wabbitwiki.com/wiki/Mites#Ear_mites

I agree that reaching out to either the same vet or finding a different one for at least some informed guidance is necessary to ensure proper and safe tx. Here is a website w/ some various links that may help with finding an alternative vet: https://wabbitwiki.com/wiki/Choosing_a_rabbit_veterinarian