Penicillin is a family of antibiotics that inhibit the synthesis of the bacterial cell wall and don’t just slow their growth, they kill bacteria. Penicillins are considered one of the safest antibiotics to take during pregnancy. They are used to treat common pneumonia and other infections caused by streptococci, skin infections, syphilis (first-line treatment Penicillin G), meningitis, listeria, and actinomyces. Allergy is the most common adverse effect including urticaria, rash, and in some cases presents a more severe reaction known as anaphylactic shock, delayed rash 1-2 weeks later, and/or superinfection due to bacterial (clostridium difficile) overgrowth in the GI (gastrointestinal system) causing enterocolitis mostly in long term therapy where the healthy intestinal flora is replenished (and here comes the importance of probiotics). Since penicillin was introduced during world war II, penicillin has provided effective treatment for a multitude of infections. Over time, many bacteria have designed ways to defeat penicillin.