Hi, thank you for the question.
First I would recommand giving her a bath as soon as you can ( you can use dawn dish soap).
If he is having a reaction to this medication you must remove all residue from the skin and fur. He may have spread the medication over other areas of the body including the face while grooming.
Besure to wash his face well with a wet slighly soapy cloth. Hydrogen peroxide is great for the initial cleaning of the wound , however I recommand switching to an anti bacterial soap and cleaning the area well twice a day.
You can apply an over the counter antibioticcream one with cortison may help with the itching.
Due to this reaction I would also not recommand using an over the counter product in the future I recommand you speak with your vet to see what they would recommand.
Technician
Practicing Veterinary Technician for 23 years. Veterinary Practice Owner, Technician Trainer