Anaphylaxis

Anaphylaxis is an acute, potentially fatal systemic reaction caused by massive mediator release from mast cells and basophils. Histamine, tryptase, prostaglandins and leukotrienes together produce vasodilation, capillary leak, bronchospasm, urticaria and gastrointestinal cramping, and the fatal pathway is either airway obstruction or circulatory collapse. The classical trigger is IgE cross-linking on mast cell surfaces after prior sensitisation. Direct non-IgE degranulation gives a clinically indistinguishable picture, historically called anaphylactoid; current nomenclature folds both into anaphylaxis and separates them as immunologic or non-immunologic.

After a parenteral exposure, onset is usually within minutes and almost always inside two hours, which is the origin of post-injection observation periods for first doses of high-risk biologics. Serum tryptase peaks roughly one to two hours after onset, so a sample during the episode and a later baseline can confirm mast cell involvement retrospectively. Epinephrine is the only first-line treatment; antihistamines and corticosteroids do nothing for airway swelling or shock.

The clinical consequence is absolute rather than graded. A confirmed anaphylactic reaction becomes a contraindication in the label and generally rules out the class, because deliberate rechallenge risks a more severe episode.

The misreadings run both ways and only one is dangerous. Local urticaria or transient flushing gets labelled anaphylaxis, needlessly removing a usable therapy. Far worse is dismissing early throat tightness, hoarseness or sudden faintness as anxiety or a vasovagal episode. Self-administration of peptides obtained outside clinical supply chains removes both safeguards at once: no observer, and no epinephrine within reach.