I'm not sure what the active ingredients of Revolution are.
I usually use Xeno 450 for lice, mites & mange mites which is Ivermectin.
Although a lot of other over the counter treatments aren't strong enough to be of much use.
I've found that Xeno is far cheaper from petdrugsonline
Pet Drugs Online - Search Results for Xeno
than most vets (£19+p&p instead of £30+ from the vets for the same product).
The weight of the Guineas defines whether you need the Xeno 450 or Xeno 50. Check the weight of your Guinea first.
***But seeing as Clifford has started on Revolution, you would need to check with the vet that the medications wouldn't conflict with each other, cause a reaction or at best just render the other medication useless.
It might be better to finish the course of Revolution on this occasion... Please discuss with your vet first-sometimes a vet can write out a prescription for a small fee & it's still cheaper to buy off of the Internet than off of your vet! Ask your vet about prices if it's the cost that's worrying you?
I know you've already had Clifford diagnosed with lice, but as a general note & for other members... if it was a fresh case I'd always get the vets diagnosis first as, mites, lice, fungal & general skin issues can be similar in symptoms to start off with & home treatments can cause an incorrect diagnosis for a first visit to the vet with the symptoms being shown.
Ps it might be better to keep all the info on Clifford's other thread, to save any confusion for any of the health experts who read them separately, I'll see if I can get an admin to merge them for you
Fingers crossed for Clifford's speedy recovery xx