Date of publication: March 11, 2016

News & Views

Meeting the challenges of individual variation in phosphate control

Hyperphosphatemia remains a problem for many patients on hemodialysis, despite advances in understanding and pharmaceuticals. This is primarily thought to be a result of non-compliance to medication and/or diet by the patient. However, a recent perspective article in the American Journal of Kidney Disease raises the possibility of factors contributing to hyperphosphatemia that are beyond the patients’ control, and suggests how individualized treatment might tackle these.[1] A study by Leung et al is also looking at more tailored treatment, adapting phosphate binder intake to match the phosphate levels consumed at different meals.[2]

Everybody is different

In his article Dr Sherman proposes a ‘triple threat’ of individual variation that may impact on a patient’s phosphate control, involving variations in dialytic phosphate removal, enteral phosphate absorption and phosphate binder efficacy.

Dialytic phosphate removal

Dialysis is accepted as an effective way of removing phosphate, however Dr Sherman highlights the variation seen between patients that is not reflected by the estimated average 800-1000mg removal during a hemodialysis session. For example, patients with a similar weight and pre-dialysis serum phosphate level had a difference of 485mg removed during dialysis (1082mg vs 597mg). The mechanisms behind this variation are not yet understood, but adapting dialysis treatment times may improve efficacy for individual patients.

Pre-dialysis serum levels also affect phosphate removal. More phosphate is removed from a patient with higher serum levels and medication calculations should take this into account.

Enteral phosphate absorption

Studies of patients on tightly controlled diets have reported a range of phosphate excretion. Dr Sherman cites a study of patients on a diet of 810 ± 27mg of phosphate a day, with a mean urinary excretion of 583mg, but a standard deviation of 216mg. This means that emphasizing dietary changes in patients with high absorption should prove the most effective.

Efficacy of phosphate binders

Phosphate binders are used as an effective addition to hemodialysis in controlling phosphorus levels, however, binding efficacy varies between patients. In a study of calcium acetate, phosphate absorption was reduced by an average 174mg (26.8mg per dose), but the binding varied from 15.0 to 36.1mg per dose. Tailoring doses to a patient’s binding efficacy would therefore improve treatment results, as could using potent binders to ensure adequate binding capacity per meal.

Dr Sherman also mentions other variables in controlling hyperphosphatemia, including the high bioavailability of ‘hidden’ phosphate additives in foods and medications, and any residual kidney function. In light of the diverse range of factors impacting on phosphate levels in ESRD patients, Dr Sherman calls for a flexible approach to treatment.

One size does not fit all

While some variations may be harder to control, a recent paper from Leung et al proposes the development of a tool to help patients adapt their medication to a variable diet.2

This 60-person study in patients undergoing peritoneal dialysis shows a large variation in dietary phosphate intake, ranging from 959 ± 249mg to 1144 ± 362mg a day. Phosphate consumption also varied hugely between meals, with the least consumed at breakfast, and the most at supper. However, phosphate binder consumption did not change to reflect this, leading the authors to suggest an impact of this discrepancy on adequate phosphate control.

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Leung et al discuss the benefits of intense educational programs in improving phosphate control, but suggest that the need for these to be ongoing is costly and time consuming. The authors propose that development of a phosphate counting application for mobile devices could assist patients in choosing an appropriate phosphate binder dose per meal.2

References

  1. Sherman R a. Hyperphosphatemia in Dialysis Patients: Beyond Nonadherence to Diet and Binders. Am J Kidney Dis. 2015:1-5. doi:10.1053/j.ajkd.2015.07.035.
  2. Leung S, McCormick B, Wagner J, et al. Meal phosphate variability does not support fixed dose phosphate binder schedules for patients treated with peritoneal dialysis: a prospective cohort study. BMC Nephrol. 2015;16:205. doi:10.1186/s12882-015-0205-3.

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