- Use of any of the following drugs within the last 6 months:systemic antibiotics (must be discontinued and avoided for 2 months prior to the study start), antifungals, antivirals or antiparasitics (intravenous, intramuscular, or oral); oral, intravenous, intramuscular, nasal or inhaled corticosteroids; cytokines; methotrexate or immunosuppressive cytotoxic agents;