Inclusion Criteria:  Subjects age 18 and older of either sex will be included. Subjects must be willing and able to provide informed consent. Subjects must have been diagnosed with ankylosing spondylitis, axial spondyloarthritis, psoriatic spondylitis or spondylitis secondary to inflammatory bowel disease by a physician and must be willing to request records to validate the diagnosis. Subjects must complete a symptom questionnaire called a BASDAI (Bath Ankylosing Spondylitis Disease Activity Index) and must have a score of four or above to indicate active disease and the potential to improve. Subjects must agree to remain on a stable treatment regimen for their joint disease for the duration of the trial and for one month before the study begins. Subjects must be willing to provide stool samples and be willing to have routine lab studies every 8 weeks during the duration of the study.  Exclusion Criteria:  Pregnant or lactating women will not be included. Subjects must not be allergic or intolerant to terbinafine. Subjects must not be taking medications that have the potential for serious interactions with terbinafine. These drugs include desipramine, cimetidine, fluconazole, cyclosporine and rifampin. Subjects must not have taken antibiotics within 3 months of starting the study drug and collecting the baseline stool specimen. Subjects with the following blood dyscrasias will not be included:  Hemoglobin <9g/dL or Hematocrit <30% White blood cell count <3.0 K/cu mm Absolute neutrophil count <1.2 K/cu mm Platelet count <100 K/cu mm Subjects with an estimated GFR ≤50 ml/min Subjects with a total bilirubin, AST, or ALT more than 1.5 times the upper limit of normal at screening.  Severe, progressive, or uncontrolled chronic liver disease including fibrosis, cirrhosis, or recent or active hepatitis. History of any lymphoproliferative disorder such as Epstein Barr virus (EBV) related lymphoproliferative disorder, history of lymphoma, leukemia, or signs and symptoms suggest of current lymphatic disease. Current malignancy or history of malignancy, with the exception of adequately treated or excised non-metastatic basal cell or squamous cell cancer of the skin, or cervical carcinoma in situ. Have or have had an opportunistic infection (e.g., herpes zoster [shingles], cytomegalovirus, Pneumocystis carinii, aspergillosis and aspergilloma, histoplasmosis, or mycobacteria other than TB) within 6 months prior to screening. Have a known infection with human immunodeficiency virus (HIV) Have current signs and symptoms of systemic lupus erythematosus, or severe, progressive, or uncontrolled renal, hepatic, hematologic, endocrine, pulmonary, cardiac (New York Heart Association class III or IV), neurologic, or cerebral diseases.