Penicillin is a substance of low toxicity but does possess a significant index of sensitization. The following hypersensitivity reactions associated with use of penicillin have been reported: Skin rashes, ranging from maculopapular eruptions to exfoliative dermatitis; urticaria; serum-sickness like reactions, including chills, fever, edema, arthralgia, and prostration. Severe and often fatal anaphylaxis has been reported (see WARNINGS). As with other treatments for syphilis, the Jarisch-Herxheimer reaction has been reported.
Pseudomembranous colitis has been reported with the use of penicillin G. Onset of pseudomembranous colitis symptoms may occur during or after antibiotic treatment (see WARNINGS).