Written by Vivian Lei
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In this large population-based study, sodium polystyrene sulfonate (SPS) use in elderly outpatients was associated with an almost 2-fold higher risk of serious adverse GI events within 30 days of initial prescription. The absolute risk increase was small, however.
Why does this matter?
SPS (brand name Kayexalate) is commonly prescribed for treatment of hyperkalemia, but prior case reports raise concern for serious GI injuries. This large population-based cohort study found a small but significantly increased risk of intestinal ischemia or thrombosis within 30 days of SPS prescription. When other options for treating hyperkalemia exist, should we really still be using this medication?
A terrible gut reaction
This was a Canadian retrospective population-based cohort study of over 20,000 patients over age 65 who received a first time prescription of SPS. The primary outcome was hospitalization or emergency department visit for adverse GI events, including intestinal ischemia/thrombosis, GI ulceration/perforation, or resection/ostomy within 30 days of initial SPS prescription. Compared to a propensity-matched cohort of similar patients who did not receive this medication, the study found 37 (0.2%) adverse GI events in the SPS group compared to 18 (0.1%) in the non-use group during the 30 day follow-up period, a significant difference with a hazard ratio of 1.94 (95% CI 1.10 – 3.41). Intestinal ischemia/thrombosis was the most common type of GI injury.
Source
Risk of Hospitalization for Serious Adverse Gastrointestinal Events Associated With Sodium Polystyrene Sulfonate Use in Patients of Advanced Age. JAMA Intern Med. 2019 Jun 10. doi: 10.1001/jamainternmed.2019.0631. [Epub ahead of print]
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Reviewed by Thomas Davis
Adverse event: bad, and present in 0.2% if reviewed cases.
But… 0.2% is a very small number and the control group had 0.1% – yes, a doubling of cases, but still… very very few in absolute numbers (as mentioned in the summary).
But what is missing for me from the summary is any mention of the benefit – was hyperK+ treated effectively. In what percentage? Any clear improvement in morbidity with SPS?
I’ve been biased against the stuff for years, I’m not asking these questions to encourage use of SPS, but to get a flesh out the info to reach a decision (or, perhaps, confirm my bias ;-).
David, the absolute harm was very small. Unfortunately, we don’t know if there was benefit in potassium lowering from this study.
I pinged Vivian Lei, who summarized this article. She said, "The study was not designed to track potassium levels before and after since it was a retrospective population-based study on outpatients prescribed SPS. They did perform some subgroup analysis on cohorts with previously known potassium levels and tried to match those groups, but it wasn’t everyone; and it was only pre-exposure potassium levels. Unfortunately, one of the limitations of the study is also that exposure is defined as the prescription itself rather than knowing whether or not the patients took the SPS or for how long.
In terms of morbidity caused by SPS, their definition of GI injury was quite broad since it was a composite outcome (intestinal ischemia/thrombosis, GI ulceration/perforation, or resection/ostomy). There was no examination of whether SPS itself improved morbidity or mortality, however.
There are a very few other studies that looked at efficacy of SPS, though. Some are questionable because they’re from around 1960 and were pretty shoddy studies. Others showed very modest effectiveness of SPS in treatment of hyperkalemia and none in a timeline relevant to an ED physician. Most studies also include other potassium-lowering therapies and low-potassium diet." Hope this helps!