Wednesday, December 26, 2012

Phosphorous Binder Equivalent Dose

Ever encountered this situation?  You're going about your daily business and discover that one of your patients on hemodialysis has an elevated phosphorous.

You skim through the list of prerequisites and see that yes, the nutritionist has been by to review dietary sources of phosphorous, the dialysis nurse has checked in on adherence to phosphorous binding medications, there's no activated vitamin D on the med list and you've explored increasing the frequency of dialysis or moving to extended nocturnal with the patient before and it's not in the cards.

Is there anything rational that can be done with the phosphorous binder dose to improve phosphorous control?  Thanks to the good work of the folks at the Frequent Hemodialysis Network (FHN) trial the answer is yes.

During the trial the investigators faced the question of whether or not changes or substitutions in multi-binder regimens represented increases or decreases in phosphorous binding capacity.  In order to answer this question the investigators combed through stool and urinary phosphorous recovery studies of individuals given various phosphate binders.   In these trials individuals were given test meals with known amounts of phosphorous.  The amount of free phosphorous appearing in the stool or urine was measured with and without binders with the difference being considered the amount of phosphorous being bound to binders in the gut.

With this information in hand the FHN group additionally looked at parallel group trials were patients on dialysis were given one of two binders and then had their doses titrated to equal serum phosphorous levels.  What emerged was a picture of the relative phosphorous binding capacity of various common binders.  Below is a table of commonly used phosphorous binders and the derived phosphate binder equivalent doses.

As you can see, all the phosphate binder equivalent doses are referenced to 1g of calcium carbonate.  So as an example, 5 tabs of 800mg sevelamer carbonate binds an equivalent amount of phosphorous (5 times 0.6 = 3) to 3 tabs of 500mg lanthanum carbonate (3 times 1.0 = 3).

Now, where ones phosphorous should ideally be is unclear (as nicely pointed out over at PBF a while back) as is the choice of agent (unless you count the realization that chronic aluminum binders where a bad deal).

Both the KDOQI and KDIGO guidelines don't endorse any one class binders over any other (again, excluding aluminum) though KDIGO gives a "2C = we suggest based on low grade evidence" that calcium based binders be restricted in the presence of arterial calcification, adynamic bone disease or persistently low PTH.  KDOQI, based on expert opinion, suggests that the amount of calcium from binders be limited to 1.5g/day (there are 200mg of calcium in a 500mg calcium carbonate tab and 169mg of calcium in a 667mg tab of calcium acetate).

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