Why can TMP/SMX (Bactrim) cause a bump in Cr without affecting GFR? I learned this fact from a tweet a while back (https://t.co/yqXaUbdB2O) and it

Why can TMP/SMX (Bactrim) cause a bump in Cr without affecting GFR? I learned this fact from a tweet a while back (https://t.co/yqXaUbdB2O) and it