Oral flea med suggestions (US)

Hi everyone! One of my regulars has a wound on the back of his ear which I suspect is from scratching fleas, mosquitoes bites, etc. I've shown a picture to my vet and they didn't think it looked infected. The main concern is getting it to heal and stopping the scratching. What are your suggestions for ORAL flea medications? I have a stockpile of the topical prescription stuff but I can't pet this one, and I tried trapping him and he somehow got out before I could get outside to secure the trap with zip ties. Thanks so much!