Anaphylactic shock was the most severe form of anaphylaxis, an allergic reaction to a trigger substance such as a food or a drug. Symptoms included respiratory and cardiovascular distress.
In 2152, Travis Mayweather had an anaphylactic reaction to an alien painkiller he was given in a hospital on Risa after he fell and was injured while climbing on a changing rockface. (ENT: "Two Days and Two Nights")
Later that year, Porthos went into anaphylactic shock when a treatment Dr. Phlox gave him was rejected by his body after he had picked up a deadly pathogen while on Kreetassa. (ENT: "A Night in Sickbay")
In 2373, The Doctor claimed that Lieutenant Torres was suffering from delayed anaphylactic shock caused by something she ate when she was found unconscious in sickbay. In order to fool Captain Janeway and Lieutenant Tuvok, he used cateline to bring Torres into a simulated anaphylactic shock. (VOY: "Darkling")
In 2375, a cytoplasmic lifeform that had attached itself to B'Elanna Torres entered an anaphylactic shock when The Doctor and the Crell Moset hologram removed it. The Doctor was able to stabilize its condition by administering stenophyl. (VOY: "Nothing Human")
In 2377, a holographic simulation of Seven of Nine went into anaphylactic shock after her Borg implants rejected a new cortical node extracted from a dead Borg drone. (VOY: "Imperfection")