Trimethoprim is an antibiotic, which is used for variety of infections. The side effects are
Stevens-Johnson syndrome, damage to the liver, rash, headache, sore throat, diarrhea,
hallucinations, and agitation. Other rare side-effect is ringing in ears, this mostly occurs in people who have depression, high blood cholesterol,
osteoporosis, or anxiety. You can see the details of side effects on the website: =http://www.ehealthme.com/ds/trimethoprim/ringing+in+the+ears.
I advice you to either change the antibiotic, or if it is necessary to take the Trimethoprim, just complete the course of antibiotic and see if the side effects subside, then it’s ok. If the ringing in ears persists, then consult an
ENT specialist for complete ear examination.