How long does antibiotic treatment for sinusitis take? Generally, oral antibiotics are required for acute sinusitis for more than two weeks, and for chronic cases, more than six weeks. Are there any side effects to taking them for that long? Of course, taking antibiotics for a long time can cause side effects such as bacterial resistance, diarrhea, mycobacterial infections, and liver and kidney damage caused by erythromycin antibiotics. But the actual incidence is very low because the daily dose is not very large. So the antibiotics given by the doctor should still be taken every day and not stopped as soon as they are slightly better. As soon as you suspect a side effect you may stop the medication and come to the doctor. If no side effects occur, you should see your doctor at least once every two weeks to decide whether or not to continue antibiotic treatment, and not to find your own medicine for a long time.