Antibiotics and Sinus Infection Make an Appointment Ask a Question Search Conditions Even if you take antibiotics according to your prescription, you may still seem to have a sinus infection. Several reasons for persistent sinus symptoms may include allergies, chronic inflammation, persistent infection, using an inappropriate antibiotic, not following medication instructions, antibiotic-resistant bacteria and/or structural abnormalities of the sinuses. A radiographic technique called a CT scan can determine the severity of a sinus infection, and sampling and culturing sinus content for bacteria or fungi can determine what's causing the infection. A CT scan can also be useful in cases of fungal infections and structural problems of the nose. Fiberoptic rhinopharyngeoscopy, a procedure that gives doctors an inside view of the nasal passage, is another way of detecting structural problems. If you follow prescription instructions and a sinus infection still won't go away, see your physician. This information has been approved by Rafeul Alam, MD (February 2014).