The Infectious Diseases Society of America suggests the following characteristics help identify patients who should be started on antibiotics: Mild to moderate sinus symptoms persisting for ≥ 10 days Severe symptoms (eg, fever ≥ 39° C, severe pain) for ≥ 3 to 4 days Worsening sinus symptoms after initially improving from a typical viral URI ("double sickening" or biphasic illness) Because many causative organisms are resistant to previously used drugs, amoxicillin / clavulanate 875 mg orally every 12 hours (25 mg / kg orally every 12 hours in children) is the current first-line drug.