A cause and a cure of hyperkalemia? The next #NephJC

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There has been a flurry of publications in the field of hyperkalemia with 3 separate trials of oral potassium binding agents within a week of each other (Sodium Zirconium in JAMA, and NEJM and Patiromer in NEJM) and a potentially related observational trial on the risks of co-trimoxazole in patients on RAAS blockade in the BMJ. With all that reading to get through, the next NephJC on Tuesday Dec 2nd will be a double whammy. We will look at the HARMONISE trial of ZS-9, and a large study of co-trimoxazole and potential associations. 

Trim-Sulfa and Sudden Death in patients receiving inhibitors of renin-angiotensin system. 

The first paper for discussion is a large, Canadian, case control series, by the Canadian Drug Safety and Research Effectiveness Network, published in the BMJ.
The hypothesis is the risk of sudden death in patients on RAAS blockade is higher following administration of specific antibiotics rather than amoxicillin. To answer their question, they searched 17 years of records representing over 1.6 million patients. They identified 39,879 with a label of sudden death and a subsequent group of 1,027 that had a prescription for the target antibiotics in the 7 days prior to dying. 
The authors write: “In the primary analysis, co-trimoxazole was associated with a significantly increased risk of sudden death within seven days relative to amoxicillin (OR 1.8 C.I 1.5-2.24)”
Ciprofloxacin was associated with a somewhat lower risk of sudden death. I found it strange that norfloxacin, which has similar QT prolonging properties to ciprofloxacin, had had no such risk. The authors speculate this observed association may be due to trimethoprim’s activity as an ENaC antagonist. There are a number of important limitations to consider. There was no indication for antibiotics recorded. Also, the cases and controls had some important differences in terms of diuretic use and co-morbidities. Only 8.2% of the cases had renal disease, the stage of which was unclassified.
The authors can only speculate about a possible mechanism involving hyperkalaemia as no K levels were obtained for any of these patients, nor any ECG to help explain the effect of ciprofloxacin. 

Harmonise: Effect of Sodium Zirconium Cyclosilicate on Potassium Lowering for 28 Days Among Outpatients With Hyperkalemia. 

ZS-9 is a zirconium silicate, a non-absorbable potassium binding agent. It is an inorganic cation exchanger crystalline with the capacity to bind both potassium and ammonium in the GI tract. Its creators tout its non-absorbable nature as the key to minimising systemic side effects. HARMONISE is a phase 3, multicenter, randomized, double-blind, placebo-controlled trial spanning 44 centres. Inclusion criteria was simply a serum K of ≥ 5.1 on 2 occasions.

Initially, 258 patients who met eligibility criteria were given ZS-9 10g three times daily. If they achieve normokalaemia within 48 hours, they were then randomized to a placebo, or increasing doses of ZS-9 once daily. The mean eGFR was 46 ml/min/1.73m2 and no ESKD patients are represented. 
Did it work? The short answer is yes. ZS-9 had a reasonable rapid rate of onset and within 2 hours, serum Potassium has dropped by −0.4 mEq/L (95% CI, −0.5 to−0.4) and was – 1.1 mEq/L by 48hours. Encouragingly, it seems generally well tolerated with some edema and hypokalemia as the doses increased. In conclusion, this is a well executed phase 3 trial and ZS-9 has potential to be a well tolerated and predictable treatment option for hyperkalemia.
The authors quite rightly point out we still have no data beyond 4 weeks, nor have we any meaningful endpoint such as mortality or hospital admissions. It is an encouraging study none the less, and should lead to FDA approval and another tool in our kit.

Full post can be seen at www.nephjc.com 

Authored by Eoin O’Sullivan.

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