A patient presents with fever, uicaria, itching and swelling followed by injection of Penicillin. It is due to

There are two clinical pictures that can result from penicillin allergy, namely acute (Type I) and sub-acute reactions (Type II) mediated by IgE and IgG antibodies respectively. The acute allergic reaction arises immediately or rapidly within minutes to an hour or two and includes sudden anaphylaxis with hypotension, bronchospasm, angioedema and uicaria. Acute reactions result from reaction with preformed IgE to penicillin as a result of previous exposure. A less dramatic picture may occur 7 to 10 days after penicillin treatment stas or 1-2 days after repeat therapy. In this setting, the picture is sub-acute and can include uicaria, fever and ahralgias or ahritis. The sub-acute reaction is caused by preformed IgG to penicillin as a result of previous penicillin treatment. The IgG antibody results in the activation of the complement reactions producing inflammation resulting in the symptoms. Ref : Ananthanarayana textbook of Microbiology 9th edition Pgno : 166,167