Penicillin and derivatives (under brand names like Amoxil) are sometimes prescribed by doctors (often unnecessarily) to deal with infections (or sometimes nothing at all) in body piercings. They may also be prescribed to reduce the post-operative risks of heavier procedures including implants and castration. While a prescription pharmaceutical in the United States and most countries, it can be ordered through foreign pharmacies and other means, and is often used without proper medical counseling.
The pictures on the right show a reaction to amoxicillin (generic of Amoxil) on a customer at a piercing studio. As well as skin rash and hives, if you notice extreme tiredness, pale or yellowed skin, bleeding (or unusual bruising), it is very important that you contact your doctor immediately. Seizures may also occur (yes, call a doctor) in rare cases, as can a sick stomach and general digestive upset. If those persist call your doctor.