I have two guinea pigs that somehow contracted mites. I have taken them to the vet for a dose of Ivermectin but due to the expense I have purchased additional Ivermectin from a local feed store and have given them another dose, that makes two doses in an eight day peroid. How long does it take to see some improvement in their skin condition? And how many doses should I give them at 7day intervals? They are pretty bad.
Thanks so much for your help.

Optional Information:
Age: 1; Female; Breed: Guinea Pig

Already Tried:
Ivermectin