Some medications (vancomycin, morphine, x-ray contrast among others) cause anaphylaxis by directly triggering mast cell degranulation.The frequency of a reaction to an agent partly depends on the frequency of its use and partly on its intrinsic properties. Anaphylaxis to penicillin or cephalosporins occurs only after it binds to proteins inside the body with some agents binding more easily than others. Anaphylaxis to penicillin occurs once in every 2,000 to 10,000 courses of treatment, with death occurring in fewer than one in every 50,000 courses of treatment. Anaphylaxis to aspirin and NSAIDs occurs in about one in every 50,000 persons. If someone has a reaction to penicillin, his or her risk of a reaction to cephalosporins is greater but still less than one in 1,000. The old radiocontrast agents caused reactions in 1% of cases, while the newer lower osmolar agents cause reactions in 0.04% of cases. Venom
Venom from stinging or biting insects such as Hymenoptera (ants, bees, and wasps) or Triatominae (kissing bugs) may cause anaphylaxis in susceptible people. Previous reactions that are anything more than a local reaction around the site of the sting, are a risk factor for future anaphylaxis; however, half of fatalities have had no previous systemic reaction. Risk factors
People with atopic diseases such as asthma, eczema, or allergic rhinitis are at high risk of anaphylaxis from food, latex, and radiocontrast agents but not from injectable medications or stings.
Richet and Portier boarded Alberts ship Princesse Alice II for ocean exploration to make collections of the marine animals.Richet and Portier extracted a toxin called hypnotoxin from their collection of jellyfish (but the real source was later identified as Portuguese man o war) and sea anemone (Actinia sulcata). In their first experiment on the ship, they injected a dog with the toxin in an attempt to immunise the dog, which instead developed a severe reaction (hypersensitivity). In 1902, they repeated the injections in their laboratory and found that dogs normally tolerated the toxin at first injection, but on re-exposure, three weeks later with the same dose, they always developed fatal shock. They also found that the effect was not related to the doses of toxin used, as even small amounts in secondary injections were lethal. Thus, instead of inducing tolerance (prophylaxis) which they expected, they discovered effects of the toxin as deadly.In 1902, Richet introduced the term aphylaxis to describe the condition of lack of protection. He later changed the term to anaphylaxis on grounds of euphony. The term is from the Greek  ἀνά-, ana-, meaning "against", and φύλαξις, phylaxis, meaning "protection". On 15 February 1902, Richet and Portier jointly presented their findings before the Societé de Biologie in Paris. The moment is regarded as the birth of allergy (the term invented by Clemens von Pirquet in 1906) study (allergology). Richet continued to study on the phenomenon and was eventually awarded the Nobel Prize in Physiology or Medicine for his work on anaphylaxis in 1913.