I had a severe allergic reaction to keflex. can i trust taking other antiobios in the future without being pre-tested? how to know if allergic again?

No penicillin: I'd avoid all penicillins and cephalosporins (of which Keflex is one), the latter having about a 5% cross reactivity to penicillin, until i can get tested. There are plenty of other antibiotic types which can be used, if needed, such as sulfa based antibiotics and quinolones. Speak to your doctor so you can be prepared in the event of an infection . Good luck!

Many options: Antibiotics are in a number of chemical classes. With a severe reaction to Keflex (also called cefazolin), you should avoid antibiotics in the cephalosporin and probably the penicillin class, as there is a higher chance of cross reactivity. Typically, we will give antibiotics in a different chemical class rather than testing. For you, examples may be clindamycin, Ciprofloxacin or vancomycin.