What Are The Side Effects Of Trimethoprim?

hi there my mum had kidney function of gfr 26 she has monthly blood tests , recently she had a a urine infection and was given trimethoprim , upon her next blood test the function had reduced to gfr 16 which was quite alarming , we were informed by the consultant this antibotic can affect the gfr readings , should we avoide this family of antibotics

thank you for your time and consideration kind reguards fiona