Can sinusitis be treated with flagyl?

Yes. Depending on the type of organism causing sinusitis. Flagyl, though, is not a first line drug.
There r better meds. Typical antibiotics include: 1. Penicillins like amoxicillin, augmentin 2. Cephalosporins like ceftin 3. Macrolides like zithromax, biaxin 4. Sulfa medicines like bactrim 5. Quinolones like avelox 6. Tetracyclines like vibramycin (doxycycline).