If you use neosporin, don't use the kind with pain killer. Apparently, something in the pain killer isn't approved for reptiles. The regular neosporin is supposed to be very good for little wounds. I'm not an expert, but I've heard this advice on other parts of this forum.
Another thing you might do is check for hot spots in your cage. If you have a UTH, you might have a hot spot on the bottom of your cage. Kingsnakes like to burrow, and if he's burrowing through his substrate to the bottom of the cage, he might be brushing against a hot spot caused by the heater. If you have a heat gun, you should do a survey of the entire bottom of the cage. If you don't have a heat gun, you might try moving a thermometer to different spots and burying it under the substrate in different spots where he might have been burrowing. You may end up needing to get a rheostat or thermostat to control your heat source. Some people say that no heat mat should ever be used without control.
I hope the vet can help. It's rough when they're sick.
Bill
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It's not how many snakes you have. It's how happy and healthy you can keep them.