Assessing a 12-month course of oral alendronate for adults with avascular necrosis of the hip: MANTIS RCT with internal pilot.

BACKGROUND: People with avascular necrosis of the hip have very limited treatment options currently available to stop the progression of this disease; this often results in the need for a hip replacement. There is some weak evidence that a class of drugs called bisphosphonates may delay the course of the disease, and this trial was commissioned and set up to provide robust evidence regarding the use of bisphosphonates in adults aged ≥ 18 years with this condition. OBJECTIVES: The aim of the Managing Avascular Necrosis Treatments: an Interventional Study ( MANTIS ) trial was to evaluate the clinical effectiveness and cost-effectiveness of a 12-month course of alendronate in the treatment of avascular necrosis. DESIGN: This was a 66-month, definitive, multisite, two-arm, parallel-group, placebo-controlled, double-blind, randomised controlled trial, with an internal pilot phase. SETTING: Eight secondary care NHS hospitals across the UK. PARTICIPANTS: Planned trial size - 280 adult patients with avascular necrosis. INTERVENTION: Participants in the intervention group received 70 mg of alendronate (an oral bisphosphonate) weekly for 12 months. MAIN OUTCOMES: The main outcomes were Oxford Hip Score at 12 months (short-term outcome) and the time to decision that a hip replacement is required at 36 months (long-term outcome). RESULTS: Twenty-one patients were recruited and randomised to receive either the intervention drug, alendronate, or a placebo-matched tablet. LIMITATIONS: This trial was principally limited by low disease prevalence. Other limitations included the late disease stage at which participants were identified and the rapid progression of the disease. FUTURE WORK: This trial was limited by a low recruitment rate. Avascular necrosis of the hip should be treated as a rare disease. Future trials would need to recruit many more sites and recruit over a longer time period, and, for this reason, a registry may provide a more effective means of collecting data pertaining to this disease. CONCLUSIONS: The MANTIS trial was terminated at the end of the pilot phase, because it did not meet its go/no-go criteria. The main issue was a poor recruitment rate, owing to a lower than expected disease prevalence and difficulties in identifying the condition at a sufficiently early stage. Those patients who were identified and screened either were too advanced in their disease progression or were already taking medication. We would not recommend that a short-term interventional study is conducted on this condition until its prevalence, geographic foci and natural history and better understood. The difficulty of acquiring this understanding is likely to be a barrier in most health-care markets. One means of developing this understanding would be the introduction of a database/registry for patients suffering from avascular necrosis of the hip. TRIAL REGISTRATION: The trial is registered as ISRCTN14015902. FUNDING: This project was funded by the National Institute for Health and Care Research ( NIHR ) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 26, No. 43. See the NIHR Journals Library website for further project information.

WHAT WAS THE QUESTION?: The Managing Avascular Necrosis Treatments: an Interventional Study ( MANTIS ) trial was designed to compare ways of treating patients with avascular necrosis who are seeking to slow down the deterioration of their condition. Alendronate is a drug routinely available across the NHS in both tablet and injection form, and doctors and scientists believe that it might prevent ongoing hip deterioration and result in fewer patients requiring a total hip replacement. WHAT DID WE DO?: This trial attempted to compare alendronate taken as a tablet with an identical-looking tablet that did not contain any of the drug (a placebo) to find out if alendronate reduced the number of patients requiring a hip replacement and having pain (compared with patients who did not get alendronate). WHAT DID WE FIND?: Patients were willing to participate in the trial but we were able to recruit only a small number to the study. The main reason for this was difficulty in identifying potentially suitable patients and approaching them at the right point in their medical care. This was more challenging than anticipated, particularly because the NHS sites and professionals that patients with this condition seek out are extremely variable in the UK. It was also difficult to locate and identify patients with the condition at an early enough stage, and before they had already started taking the drug. WHAT DOES THIS MEAN?: More information on patients with this rare condition, such as NHS referral pathways, and an understanding of how the condition progresses may help to improve our understanding of this patient group. This information could also help us determine whether or not there is scope to carry out the study in a different way that might enable these patients to be more easily identified.

Single-cell O2 exchange imaging shows that cytoplasmic diffusion is a dominant barrier to efficient gas transport in red blood cells.

Disorders of oxygen transport are commonly attributed to inadequate carrying capacity (anemia) but may also relate to inefficient gas exchange by red blood cells (RBCs), a process that is poorly characterized yet assumed to be rapid. Without direct measurements of gas exchange at the single-cell level, the barriers to O2 transport and their relationship with hematological disorders remain ill defined. We developed a method to track the flow of O2 in individual RBCs by combining ultrarapid solution switching (to manipulate gas tension) with single-cell O2 saturation fluorescence microscopy. O2 unloading from RBCs was considerably slower than previously estimated in acellular hemoglobin solutions, indicating the presence of diffusional barriers in intact cells. Rate-limiting diffusion across cytoplasm was demonstrated by osmotically induced changes to hemoglobin concentration (i.e., diffusive tortuosity) and cell size (i.e., diffusion pathlength) and by comparing wild-type cells with hemoglobin H (HbH) thalassemia (shorter pathlength and reduced tortuosity) and hereditary spherocytosis (HS; expanded pathlength). Analysis of the distribution of O2 unloading rates in HS RBCs identified a subpopulation of spherocytes with greatly impaired gas exchange. Tortuosity imposed by hemoglobin was verified by demonstrating restricted diffusivity of CO2, an acidic gas, from the dissipative spread of photolytically uncaged H+ ions across cytoplasm. Our findings indicate that cytoplasmic diffusion, determined by pathlength and tortuosity, is a major barrier to efficient gas handling by RBCs. Consequently, changes in RBC shape and hemoglobin concentration, which are common manifestations of hematological disorders, can have hitherto unrecognized and clinically significant implications on gas exchange.