Thanks funkyfish.
We are ;in the US.
No vet for this one. He is a barn cat. We love him but we treat him ourselves. The penicillin is for animals (from tractor supply) We did shave the site, drain the cut, clean and peroxided. We were thinking of an injection of the antibiotics and copper sulfide powder.
Just need the dosage. I did find a site that suggested 1/2 ml.