Assessing Bone Calcium Content in Children With Kidney Disease Treated With Two Different Medicines

Overview

This is an open label, time series trial. The trial is likely to be single centre (additional sites will only be opened if necessary) and will involve 25 children with chronic kidney disease (stage 3b, 4-5) or on dialysis. The overall aim of this trial is to explore the viability of the Ca isotope ratio measured by dual-tracer stable Ca isotope method as a measure of bone mineral (Ca) content, and to evaluate how it changes in response to two commonly used medications that either contain Ca (calcium carbonate) or do not (sevelamer carbonate). Both calcium carbonate and sevelamer carbonate are routinely used in children, but their effect on the bone mineral content (measured by the Ca isotope ratio) has not been studied. This short-term trial will provide proof-of-concept data to determine the utility of the Ca isotope fractionation technique in guiding medication usage in children with CKD and on dialysis. These data will inform a potential future randomised trial that utilises the calcium isotope fractionation technique to adjust the calcium intake (through diet and different medications, including vitamin D analogues) and monitor changes in important patient level outcomes such as fractures and bone mineral density on DXA scan. Participants will be administered sevelamer carbonate first for 16 weeks and then will switch to calcium carbonate for 12 weeks. Participants may need to change medication earlier than 16 weeks at the clinician's discretion based on their calcium levels on routine blood tests. Calcium isotope levels will be measured in blood and urine samples for up to 28 weeks. Isotopes levels in faeces and dialysis fluid samples may also be measured. This is not a Clinical Trial of an Investigational Medicinal Product (CTIMP).

Lay Summary of Background and Rationale: The growing bones of children need calcium in order to mineralise (become strong). Children with kidney failure (called chronic kidney disease; CKD) or on dialysis can often be calcium deficient. They are given medications with extra calcium to help their bones mineralise. However, there is currently no practical way of measuring bone mineralisation. Doctors may perform special x-rays, but it takes many months before any bone structure problems become apparent on X-rays. Doctors giving children additional calcium do not know how much to give. Sometimes children are given too little and their bones do not mineralise adequately, or they are given too much, and the excess calcium is deposited in their arteries causing vascular calcification. Timely and practical ways of measuring bone mineralisation are needed so doctors can accurately determine the amount of calcium containing medicines they give. The CAL-BAL trial will evaluate a novel potential biomarker of bone mineralisation: the calcium isotope ratio (δ44/42Ca) which will be measured in blood and urine. The trial will collect information on δ44/42Ca for patients with CKD or on dialysis for 28 weeks. It will measure how δ44/42Ca changes when a patient switches from a medicine containing calcium to one not containing calcium. It will also evaluate the association between δ44/42Ca and established biomarkers of bone formation and repair. The data collected in CALBAL will not by itself allow doctors to decide whether δ44/42Ca is good biomarker of bone mineralisation. However, it will provide additional biological and clinical information that will further clarify its usefulness as biomarker for further research. Together with information from previous studies done by the Chief Investigator which measured the typical δ44/42Ca of healthy children and children with CKD and on dialysis, the data collected in CAL-BAL may inform the design of a future randomised trial of standard-of-care compared to an approach where δ44/42Ca results are used to prescribe the amount of medicine containing calcium children with CKD or on dialysis are given.