Will omnicef work on kidney infection? was switched to omnicef from bactrim (sulfamethoxazole and trimethoprim) ds because of rash and shaking.

Probably OK, but...: Bad luck with the allergic reactions. Antibiotic effectiveness for any infection depends on the bacteria causing it and which antibiotics are active against it. If you had a positive urine culture that was tested and found susceptible to cefdinir (Omnicef®), it will work well. If such testing wasn't done, you'll have to wait and see how it works. Discuss with the doc who prescribed it. Good luck!