My GSD's demodex responded to Ivomec. Incidentally, my own "rash" went away as her mange did. I gave it once a week, since I got recommendations between daily and every 3 weeks

I did follow the dosage recommendations though: Ivomec 1% solution, given orally at the rate of 1/10ml per 10 lbs.
You can buy Ivomec at the farm store, it's injectable ivermectin for cattle and swine. You'll need a syringe with needle with 1/10cc (or ml) markings to get the Ivomec out of the bottle and to measure it, and a bigger syringe to squirt the Ivomec into so you can mix it with about 2ml of broth or something else that's tasty. As in, suck about 2ml of tasty liquid into the bigger syringe, then squirt the Ivomec from the smaller syringe into that.
Years ago, I was taught to give liquids between the gumline and the cheek of an animal to keep the stuff from going down the airway. So, that's what I did with Mink, and it worked beautifully. I made her sit by my side, facing the same way, then I cupped my left hand around her face and pulled the corner of her lips out enough to stick the syringe in. Then I squirted the stuff in her mouth, slowly enough so she could lick and swallow (else it drips out as you push the plunger).
Ivomec is said to be terribly bitter, so that's where the tasty juice comes in. Broth or the liquid from a can of peas or corn will work fine, if your dog is anything like mine. Top it off with a saucerful of the same afterwards, and the whole thing gets to be a treat session rather than a yucky, forceful medicating experience.
I think Ivomec needs to be or should be kept in the fridge.
That's the condensed version of the advice I got here when I asked about Mink - can't beat this forum for help!!