I'm allergic to penicillen. which levaquin dosage is stronger to take for a severe sinus infection? is it 500 mg or 750 mg once daily for 10 days?

Maybe OK, but...: Most sinusitis doesn't need antibiotic treatment. If needed, levofloxacin probably would be effective, but other antibiotics usually are preferable in pen-allertic person (e.g. doxycycline, clindamycin, cefixime). If levofloxacin, either of these doses should be OK. But don't treat yourself with left over antibiotic: see a doctor to confirm the diagnosis and prescription.

Depends: It depends on the nature of the infection and physician preference. Sometimes, antibiotic courses of 3-6 weeks are required to adequately treat the sinus cavities. Because of this, antibiotic selection and dosages must be selected with care in order to reduce side effects, adverse outcomes of antibiotic treatment and the development of resistant bacteria. PCN allergy should always be confirmed.