ZS-9

File:ZS-9 structure.png Crystal structure of ZS-9. Blue spheres  =  oxygen atoms, red spheres  =  zirconium atoms, green spheres  =  silicon atoms.
Systematic (IUPAC) name
Silicic acid, sodium zirconium(4+) salt (3:2:1), hydrate
Clinical data
Legal status	US: Investigational Investigational
Routes of administration	Oral
Pharmacokinetic data
Bioavailability	Not absorbed
Excretion	Stool
Identifiers
CAS Number	242800-27-7
ATC code	none
UNII	D652ZWF066
Chemical data
Formula	(2Na·H2O·3H4SiO4·H4ZrO6)n

ZS-9 (sodium zirconium cyclosilicate) is a selective oral sorbent that traps potassium ions throughout the gastrointestinal tract. It is being developed by ZS Pharma and AstraZeneca for the treatment of hyperkalemia (elevated serum potassium levels).

Background

Main article: Hyperkalemia

Hyperkalemia occurs in 3 to 10% of hospitalized patients but is often mild. Hyperkalemia can arise from impaired renal function, potassium-sparing diuretics and renin-angiotensin system blockers (e.g., ACE inhibitors, angiotensin receptor blockers, spironolactone) and diabetes mellitus.

There is no universally accepted definition of what level of hyperkalemia is mild, moderate, or severe. However, if hyperkalemia causes any ECG change it is considered a medical emergency due to a risk of potentially fatal abnormal heart rhythms (arrhythmia) and is treated urgently. serum potassium concentrations greater than 6.5 to 7.0 mmol/L in the absence of ECG changes are managed aggressively.

Hyperkalemia, particularly if severe, is a marker for an increased risk of death. However, there is disagreement regarding whether a modestly elevated serum potassium level directly causes significant problems. One viewpoint is that mild to moderate hyperkalemia is an secondary effect that denotes significant underlying medical problems. Accordingly, these problems are both proximate and ultimate causes of death, and adjustment of potassium may not be helpful. Alternatively, hyperkalemia may itself be an independent risk factor for cardiovascular mortality.

Several approaches are used in treatment of hyperkalemia,. In October 2015, the U.S. Food and Drug Administration (FDA) approved patiromer which works by binding free potassium ions in the gastrointestinal tract and releasing calcium ions for exchange. Previously, the only approved product was sodium polystyrene sulfonate (Kayexalate), an organic ion-exchange resin that nonspecifically binds cations (e.g., calcium, potassium, magnesium) in the gastrointestinal tract. The effectiveness of sodium polystyrene sulfonate has been questioned: a study in healthy subjects showed that laxatives alone were almost as effective in increasing potassium secretion as laxatives plus Kayexalate. In addition, use of sodium polystyrene sulfonate, particularly if formulated with high sorbitol content, is uncommonly but convincingly associated with colonic necrosis.

Mechanism of action

File:ZS-9 binding ions.png

Cross-sections of ZS-9 pores with three different ions (K⁺ = potassium, Na⁺ = sodium, Ca²⁺ = calcium). The specifity for potassium is thought to be caused by the diameter and composition of the pores, which resembles potassium channels.

ZS-9 is a zirconium silicate. Zirconium silicates have been extensively used in medical and dental applications because of their proven safety. 11 zirconium silicates were screened by an iterative optimization process. ZS-9 selectively captures potassium ions, presumably by mimicking the actions of physiologic potassium channels. ZS-9 is an inorganic cation exchanger crystalline with a high capacity to entrap monovalent cations, specifically potassium and ammonium ions, in the GI tract. ZS-9 is not systemically absorbed; accordingly, the risk of systemic toxicity may be minimized.

Clinical studies

A phase 2 clinical trial in 90 patients with chronic kidney disease and mild-to-moderate hyperkalemia found a significantly greater reduction in serum potassium with ZS-9 than placebo. ZS-9 was well tolerated, with a single adverse event (mild constipation).

A double-blind, phase 3 clinical trial in 753 patients with hyperkalemia and underlying chronic kidney disease, diabetes, congestive heart failure, and in patients on renin-angiotensin system blockers compared ZS-9 with placebo. Patients were randomly assigned to receive either ZS-9 (1.25 g, 2.5 g, 5 g, or 10 g) or placebo 3 times daily for 48 hours (acute phase). Patients who achieved normokalemia (serum potassium of 3.5-4.9 mmol/L) were randomly assigned to receive ZS-9 or placebo once daily for 12 additional days (maintenance phase). At the end of the acute phase, serum potassium significantly decreased in the 2.5 g, 5 g, and 10 g ZS-9 groups. During the maintenance phase, once daily 5 g or 10 g ZS-9 maintained serum potassium at normal levels. Adverse events, including specifically gastrointestinal effects, were similar with either ZS-9 or placebo.

A double-blind, phase 3 clinical trial in 258 patients with hyperkalemia and underlying chronic kidney disease, diabetes, congestive heart failure, and in patients on renin-angiotensin system blockers compared ZS-9 with placebo. All patients received 10 g ZS-9 three times daily for 48 hours in the initial open-label phase. Patients who achieved normokalemia (serum potassium 3.5-5.0 mEq/L) were randomly assigned to receive either ZS-9 (5 g, 10 g, or 15 g) or placebo once daily for 28 days (double-blind phase). 98% of patients (n=237) achieved normokalemia during the open-label phase. During the double-blind phase, once daily 5 g, 10 g, and 15 g ZS-9 maintained serum potassium at normal levels in a significantly higher proportion of patients (80%, 90%, and 94%, respectively) than placebo (46%). Adverse events were generally similar with either ZS-9 or placebo. Hypokalemia occurred in more patients in the 10 g and 15 g ZS-9 groups (10% and 11%, respectively), versus none in the 5 g ZS-9 or placebo groups.

Regulatory

In the United States, regulatory approval of ZS-9 was rejected by the Food and Drug Administration in May 2016 due to issues associated with manufacturing.

See also

• Patiromer, another potassium binder