Can cephalexin be used to treat a sinus infection?

If your doctor ordered this for you, the answer is yes, it will help...

You probably have leftover cephalexin and don't want to see a doctor or buy more medicine, right, so you want to know if it's ok to use it? I don't know, call your pharmacist. Bear in mind though that when antibiotics are prescribed, you are supposed to take all of them for the whole 7-10 days, so you shouldn't have any left over. And if you do, remember that a partial course of antibiotics can cause the germ to gain immunity, making treatment that much more difficult. See a doctor.