How can I avoid another allergic reaction to an antibiotic medicine if allergic to penicillin?

Avoidance. If one is allergic to penicillin then avoidance of penicillin like medications is a requirement. Other classes of antibiotics should be fine but because an individual has one drug allergy they may be at risk for reactions to other classes of drugs. One should also be very clear that moving forward that antibiotics are needed.