Treatment of Osteogenesis Imperfecta With Parathyroid Hormone and Zoledronic Acid

Osteogenesis imperfecta (OI) is an inherited skeletal disorder characterised by increased risk of fragility fractures. Bisphosphonates are frequently prescribed for adult patients with OI with the aim of preventing fractures but the evidence base for efficacy is poor. Recent evidence suggests that the bone anabolic agent teriparatide (TPTD) increases bone mineral density (BMD) and may have the potential to prevent fractures in OI.

The purpose of the TOPaZ Trial is to investigate if a a two-year course of teriparatide (TPTD) followed by antiresorptive therapy with a single infusion of zoledronic acid (ZA) in adults with OI reduces the proportion of patients who experience a fracture as compared with standard care.

The trial has a number of secondary objectives which aim to investigate if a two-year course of TPTD followed by antiresorptive therapy with a single infusion of ZA in adults with OI reduces the total number of fractures, reduces the risk of vertebral fractures; or affects bone pain, quality of life and functional status as compared with standard care. There is also a planned mechanistic analysis to understand which baseline characteristics of adults with OI, such as age, clinical subtype of OI, genetic diagnosis, bone turnover, BMD, and previous treatment influences the occurrence of fractures and/or the response to treatment

Adult patients with a clinical diagnosis of OI who are willing and able to give informed consent and who do not have contraindications to the study medications will be recruited from participating sites. Participants will be randomised 1:1 to receive either standard care for the duration of the trial or TPTD for 24 months followed by a single infusion of ZA, or another antiresorptive agent in the event that ZA is contraindicated. Exclusion criteria include: current or previous treatment with an investigational (non-licensed experimental) drug with effects on bone metabolism, contraindication to TPTD or ZA, women of childbearing potential not using highly effective methods of contraception, pregnancy, women that are breastfeeding or age <18 years.

Participants will attend recruiting centres for a Baseline/Screening visit, at 12 months, 24 months and at the end of the trial for formal study visits with telephone calls every 6 months from a site research nurse. Participants randomised to TPTD will also attend recruiting centre at regular intervals during the 24 month treatment period to collect new supplies of TPTD.

The baseline assessment will include dual energy x-ray absorptiometry (DEXA), spine x-rays, safety bloods, medical and fracture history, pain (brief pain inventory, BPI) and quality of life (SF36, HAQ, EQ5D, PSQI). Blood will be taken for genetic analysis and for analysis of biochemical markers of bone turnover. In some centres, a high resolution quantitative CT scan (HRQCT) of the wrist and tibia will be performed. Participants will be seen after 12 months when bloods, questionnaires and HRQTC will be repeated; at 24 months when bloods, questionnaires, DEXA and HRQCT will be repeated. At the end of the study participants will undergo DEXA, spine x-rays, HRQCT and bloods and questionnaires will be repeated. Information on adverse events and fractures will be collected throughout the study and participants suspected to have fractures will have x-ray or other imaging to confirm the presence of fractures.