Beta-lactam allergy is the most prevalent drug allergy. Drug eruption is the most common symptom whereas life-threatening anaphylaxis is rather rare. A recently published study (Journal of Allergy and Clinical Immunology, January 2011, Vol. 127, p. 218-222) described the safety of a 2-day oral beta-lactam challenge in penicillin-allergic patients, disregarding their penicillin skin test results. In the proposed study the investigators will similarly challenge beta-lactam allergic patients, both children and adults for an extended (5 days) period of time. The study will include patients with a history of a skin rash following beta-lactam administration as well as patients who cannot provide any data on their presumed allergic reaction, disregarding their penicillin skin test results.

Inclusion Criteria:

• History of skin rash following the administration of beta-lactam antibiotic
• Patients with a diagnosis of penicillin allergy who have no data on the nature of the symptoms that have eventually resulted in establishing this diagnosis

Exclusion Criteria:

• Patients in whom the rash appeared within 1 hour after the last dose of the drug
• Patients who also developed other anaphylactic symptoms
• Patients who had a life-threatening rash such as Stevens-Johnson Syndrome, Toxic Epidermal Necrolysis or DRESS.
• Pregnancy