Hey there,
Sorry to see about Kovu licking himself obsessively. I can see that he has really made his skin very inflamed. A somewhat common problem in cats called Eosinophilic Granuloma Complex (EGC) comes to mind when I see this photo, specifically because the middles and backs of his hind legs are affected. If this is the cause, it likely has nothing to do with his seizure disorder or phenobarbital. These lesions can easily develop secondary bacterial infections though, which may require antibiotics.
Tackling EGC often involves a bit of trial and error to figure out what works best for each cat. Some cats only ever break out once or twice in their lives, and some cats need to have a special hypoallergenic diet, consistent flea control, and allergy medications throughout their whole lives. It is generally something that can be managed well once it is under control.
Here is a link for more information about EGC:
https://veterinarypartner.vin.com/default.aspx?pid=19239&id=4951528I'd recommend getting Kovu into his veterinarian in the next 48 hours to have him examined and his itchiness addressed. They can talk to you more about their clinical findings with Kovu and what diagnostics are needed and what treatment is best for him.
I hope this helps. Thanks for using PetCoach.