My brother is taking amoxicillin for a sinus infection. he is shivering a lot and feeling weakness and dehydration. why? how can i prevent this?

Go back to MD: I don't know how long your brother has been on antibiotics and how old, but if after a full 24 hours on the antibiotics and 48 at the most, if he is not better, you have to consider resistance to that antibiotics and for a penicillin, it is high. For sinus infection to be causing what seems like fever and chills and picture of sepsis it seems bad, so go back to your doctor please.