I got a quick lesson about oral antibiotics several years ago. After a dental procedure, he gave me an antibiotic. After a couple of days, I got a rash on both arms. Then dark brown spots on my palms & soles of my feet. I saw a dermatologist who prescribed another medication. When I picked it up & read the big bold information that came with it : "Do not take this medication if you are diabetic," I thought, "Hmmmm, the doctor knows I'm diabetic....." I told the pharmacist, "No thanks."
I decided to do nothing & stop taking the antibiotic. The spots on my palms turned into big fluid-filled blisters that itched terribly. When they broke open, big chunks of skin were hanging on my palms like a mummy. I could see new skin growing. What I thought indicated something seriously wrong was actually a healing process. In two weeks, I had brand new palms. I haven't taken antibiotics ever since - 20 more root canals, 12 extractions & gum surgery. I don't even mention it to dentists; when they ask, I just say, "Yes, I'm taking the antibiotics as directed" because they always say, "I'll prescribe a different antibiotic."
No problems since.