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I am sorry to hear you are worried about your cat. My name is Rebecca. I am a veterinarian and will do my best to help.
If he is scratching it, it must be itchy. In addition to the antibiotic cream you are using, I might also try applying an ointment that contains cortisone, such as Cortaid or Cortizone 10.
If it continues not to heal, I would next do a "skin scraping" where I get cells from the area of hair loss, and examine it under a microscope for infection, parasites, fungus, etc. This could be ringworm, a fungal skin infection. You could ask your vet to shine a Woods Light on it; ringworm usually glows fluorescent green under these special black lights (ultraviolet).
Let me know what other questions you have.
How is your cat doing? I hope you were able to see what I sent. Can I help with or answer anything else?
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