A Phase II Study Evaluating SB-751689 in Post-Menopausal Women With Osteoporosis.

Inclusion: * Informed consent: Subject is willing and able to provide written informed consent. * Menopausal status: Ambulatory female aged \< 80 years at screening and \>5 years postmenopausal. * T-Score: A subject with either no or only one prevalent vertebral fracture is eligible for inclusion if she satisfies one of the following T-score requirements: If no prevalent vertebral fracture subject must have an absolute BMD value consistent with a T-score of less than or equal to -2.5 and greater than -4.0 at either the femoral neck, total hip, trochanter, or lumbar spine, or If one prevalent vertebral fracture subject must have an absolute BMD value consistent with a T-score of less than or equal to -2.0 and greater than -4.0 at either the femoral neck, total hip, trochanter, or lumbar spine. * Suitable vertebra: Two or more vertebra in the range of L1 to L4 that are suitable for BMD measurement by DXA. * Protocol compliance: Subject who, in the opinion of the investigator, is willing and able to comply with the requirements of the protocol. Exclusion: * T-Score: Has an absolute BMD value consistent with a T-score less than or equal to -4.0 at either the femoral neck, total hip, trochanter, or lumbar spine. * Vertebral fractures: Has \>1 prevalent vertebral fracture at the screening visit. * Non-vertebral fractures: Any previous non-vertebral osteoporosis related/fragility fracture after age 40. * Spine deformity: Significant spine deformity which would preclude DXA/QCT assessments. * BMI: BMI ≥33kg/m2. * Bone metabolic diseases: Other than osteoporosis, history or concurrent diseases affecting bone metabolism (e.g., osteomalacia, hyperparathyroidism, hyperthyroidism). * GI disease: History of major upper gastrointestinal disease * Malabsorption: Active or history of malabsorption (e.g., history of celiac disease, irritable bowel syndrome or inflammatory bowel disease). * Liver disease: Past or current history of liver disease or known hepatic or biliary abnormalities, (with the exception of previously documented diagnosis of Gilbert's syndrome). * Rheumatoid arthritis: Active disease or history of rheumatoid arthritis. * Nephrolithiasis: History of or active nephrolithiasis (kidney stones). * Osteosarcoma risk: Subjects at increased risk of osteosarcoma such as those with Paget's disease of bone or any prior external beam or implant radiation therapy involving the skeleton. * Malignancy: Malignant disease diagnosed within the previous 5 years (except resected basal cell cancer). * Biological abnormalities: Any clinically relevant biological abnormality found and/or volunteered at screening (other than those related to the disease under investigation) which, in the opinion of the investigator, is clinically significant and would preclude safe participation in this study. * Surgical and medical conditions: Presence of the following conditions within six months prior to screening: myocardial infarction, coronary bypass surgery, coronary artery angioplasty, unstable angina, cardiac arrhythmia, clinically evident congestive heart failure, or cerebrovascular accident. * Glomerular filtration rate: Glomerular filtration rate (GFR) \<35 mL/min as calculated by the Modification of Diet in Renal Disease (MDRD) equation as follows: GFR (mL/min/1.73 m2) = 186 x (Serum creatinine mg/dL)-1.154 x (Age)-0.203 x (0.742 if female) x (1.210 if African American) (conventional units). * QT/QTc prolongation: A marked baseline prolongation of QT/QTc interval (e.g., QTc interval ≥450 msec on the Screening ECG). * Torsades de Pointes: A history of risk factors for Torsades de Pointes (e.g., heart failure, hypokalemia, family history of Long QT Syndrome). * Liver chemistries: Liver chemistries \[aspartate aminotransferase (AST), alanine aminotransferase (ALT) or total bilirubin\] exceeding 2-fold the upper limit of the laboratory-specified reference range, at screening. * Abnormal serum calcium: Serum calcium (total or albumin-adjusted) outside the central laboratory reference range at the screening visit. * Abnormal PTH: PTH (intact or whole) outside the normal range. * Abnormal creatine phosphokinase: Creatine phosphokinase (CPK) outside the normal range. * Abnormal alkaline phosphatase: Alkaline phosphatase outside of the normal range. * Thyroid hormone replacement: Subjects receiving thyroid hormone replacement therapy must have a TSH level checked. Subjects will be excluded if TSH levels are \<0.1 or \>10.0mIU/L. However, subjects will not be excluded if TSH is in the range 0.1-4.5 mIU/L. If TSH is \>4.5 and ≤10.0mIU/mL, measure T4 and exclude the subject only if the T4 is outside the normal range. * Vitamin D deficiency: Vitamin D deficiency (serum 25-hydroxy vitamin D \< 20ng/mL, equivalent to 50nmol/L) at screening. Subjects can undergo vitamin D repletion as per local practice and be re-screened once only for vitamin D levels within the 6-week screening period. They will remain excluded if the re-screened value is \< 20ng/mL. * Previous strontium or IV bisphosphonate: Any previous treatment with strontium ranelate or intravenous bisphosphonate. * Oral bisphosphonates: Any previous treatment with an oral bisphosphonate as follows: any treatment within the last six months * one month cumulative treatment within the last 12 months * three months cumulative treatment within the past two years, or * two years cumulative treatment within the past five years. * Fluoride: Treatment with fluoride (dose greater than 10mg/day) within the previous 5 years for osteoporosis. * Digoxin: Current therapy with digoxin. * Bone metabolism drugs: Treatment with other drugs affecting bone metabolism within the last six months prior to screening: Chronic systemic corticosteroid \[e.g., glucocorticoid, mineralocorticoid\] treatment of no more than 2 intra-articular injections within the past year or use of oral, parenteral, or long-term, high-dose inhaled corticosteroids. Treatment with any topical corticosteroid will not exclude the subject from participating. Hormones \[e.g., estrogens/"natural estrogen preparations"(except for nonsystemic vaginal treatment), 19-norprogestins, SERMs such as raloxifene, anabolic steroids/androgens such as dehydroepiandrosterone (DHEA) or its sulfated form (DHEAS), nandrolone, tibolone, active vitamin D analogs/metabolites such as 1,25-dihydroxy vitamin D (calcitriol) or 1alpha-hydroxyvitamin D3 (1-alpha hydroxycholecalciferol), calcitonin\]. Calcineurin inhibitors \[e.g., cyclosporine, tacrolimus\] or methotrexate. * Previous anabolic agents: Treatment with PTH, PTH analogues or similar anabolic agent for osteoporosis within the last two years. * Contraindications: Contraindications to therapy with calcium or vitamin D. * Pregnancy: Women who are pregnant are not allowed in this study. * Interfering medications: Vitamin A in excess of 10,000 IU per day, heparin, or lithium, or anticonvulsant medications except benzodiazepines. * Investigational drug exposure: Administration of any investigational drug within 90 days preceding the first dose of the study drug. * Substance abuse: History or current evidence of drug or alcohol abuse within the previous 12 months. * Problems swallowing: Inability to swallow a tablet whole. The following exclusion criteria do not apply to subjects allocated to the open-label teriparatide group: * Calcium channel blockers: Current therapy with calcium channel blockers diltiazem and verapamil. * Oral Azole Antifungals: Current therapy with any oral azole antifungal. * Immunosuppressants: Current therapy with cyclosporine or oral tacrolimus. * Ritonavir: Current therapy with ritonavir. * Quinidine: Current therapy with quinidine. * Macrolide Antibiotics: Subjects anticipated to require chronic use of macrolide antibiotics. * Alendronate Contraindications: Contraindications to therapy with alendronate. Additional Exclusion Criteria for Subjects Recruited at QCT Sites * Hip surgery: History of hip surgery resulting in a metal implant on either the left or right side that would cause an artefact on a QCT scan. Additional Exclusion Criteria for Teriparatide Subjects * Teriparatide contraindications: Contraindications to therapy with teriparatide according to locally approved datasheet.