'anaphylactically' originates from 'anaphylactic', which is derived from the Greek word 'anaphylaxis', where 'ana-' meant 'against' and 'phylaxis' meant 'protection'.

'anaphylaxis' was adopted into English from French 'anaphylaxie', which itself came from Greek, and the adverbial form 'anaphylactically' was later formed in English.

Initially, it referred specifically to the process of losing protection (against something), but now it refers to anything relating to or characteristic of anaphylaxis, especially severe allergic reactions.