Teriparatide (Forsteo) Treatment in Postmenopausal Women: Mechanism of Action

Inclusion Criteria Subjects must: * Have a bone mineral density T-score (at the lumbar spine or total hip) of less than or equal to -2.5 * Be female * Be at least 5 years post menopausal (more than 5 years since their last menstrual period) but \<85 years old. * Be ambulatory * Be able and willing to participate in the study and provide written informed consent * Have a serum 25(OH)2 vitamin D3 \>50 nmol/L (after vitamin D3 loading) Exclusion Criteria Patients will not be admitted to the study if they exhibit any of the following: * Evidence of a clinically significant organic disease which could prevent the patient from completing the study * A body mass index less than 18 or greater than 35 * Abuse of alcohol or use illicit drugs (information obtained from medical history) or who consumed more than 4 servings of any alcoholic beverage one day prior to the visit (i.e., subjects who might be binge drinkers) * Any history of cancer within the past 5 years excluding skin cancer non melanomas * Any history of ongoing conditions or diseases known to cause abnormalities of calcium metabolism or skeletal health including Paget's disease of bone * Chronic renal disease (as defined by an estimated glomerular filtration rate of ≤ 30mL/min) * Acute or chronic hepatic disease * Malabsorption syndromes * Hyperthyroidism as manifested by TSH outside the lower limit of the normal range * Hyperparathyroidism * Hypocalcemia or hypercalcemia * Osteomalacia * Cushing's syndrome * Current use of glucocorticoid therapy * A corrected serum calcium less than 2.2 mmol/L and a PTH above 100 ng/L (that persists after testing and treatment for vitamin D deficiency) * A history of any known condition that would interfere with the assessment of DXA at either lumbar spine or femoral neck * Markedly abnormal clinical laboratory parameters that are assessed as clinically significant by the investigator * Any previous use of bisphosphonate * Use any of the following medications within 12 months of starting study drug * Any fluoride with the exception of use for oral hygiene * Strontium Ranelate * Other bone agents (e.g. SERM, isoflavones, HRT) * Participation in another clinical trial involving active therapy 3 months prior to enrolment * Less than 5 years since menopause * Bilateral fractures in the measurement regions (hip, tibia and forearm) * Recent fracture within the last 12 months * Prior radiation therapy which may involve the skeleton * Hypersensitivity to teriparatide or any of its excipients * Unexplained elevations of alkaline phosphatase * Any known contraindication to the use of teriparatide