Which of the following is the most common allergic reaction to penicillin?

The most common manifestation of penicillin allergy is a maculopapular or urticarial rash (hives), occurring in approximately 1 to 5% of patients. It is typically a delayed (Type IV) or IgE-mediated (Type I) hypersensitivity reaction. Stevens-Johnson syndrome (SJS) is a severe, life-threatening mucocutaneous reaction but is RARE (less than 1 in 10,000 exposures), not the most common reaction. Nausea and vomiting are gastrointestinal side effects (not allergic reactions). Dry mouth is not a typical penicillin reaction. Patients with a history of SJS or toxic epidermal necrolysis should NEVER receive penicillin again. The most common = rash; the most severe = anaphylaxis or SJS.