Commonly referred to as a sinus infection, sinusitis is an inflammation of the sinuses that is frequently brought on by allergies or infections. Antibiotics like penicillin are frequently used as the first line of treatment for sinusitis, especially bacterial sinusitis. However, what if you have a penicillin allergy? Treatment for sinusitis can be more difficult if you have a penicillin allergy, but it's not a hopeless situation. For those who are unable to take penicillin, there are a number of efficient substitute therapies and drugs available.