ZS Pharma & AstraZeneca v. Ascent & Hetero: LOKELMA® Patent Ends in Consent Judgment
ZS Pharma, Inc. and AstraZeneca Pharmaceuticals, LP sued Ascent Pharmaceuticals, Inc. and Hetero Drugs, Ltd. in Delaware federal court over US11738044B2, protecting LOKELMA® (sodium zirconium cyclosilicate) oral suspension used to treat hyperkalaemia. The case resolved via a court-entered consent judgment after 607 days — a resolution structure that typically signals a negotiated entry date arrangement between the innovator and the ANDA filer.
LOKELMA® ANDA litigation ends on agreed terms after 607-day Delaware battle
On 20 October 2023, ZS Pharma, Inc. and AstraZeneca Pharmaceuticals, LP filed a Hatch-Waxman patent infringement action in the District of Delaware (Case No. 1:23-cv-01188) against Ascent Pharmaceuticals, Inc. and Hetero Drugs, Ltd. The asserted patent, US11738044B2, covers the active pharmaceutical ingredient sodium zirconium cyclosilicate and the oral suspension formulations marketed as LOKELMA® 5 g and 10 g per packet — a potassium-binding agent indicated for adults with hyperkalaemia.
The case closed on 18 June 2025 following a consent judgment signed by Judge Jennifer L. Hall on 8 May 2025. Notably, Hetero Drugs, Ltd. had been removed from the litigation at an earlier stage: a stipulation was so ordered by Judge Williams on 19 October 2022 in the related member case (No. 22-1099-JLH), suggesting Hetero resolved its position separately and prior to the main consent judgment. A consent judgment in Hatch-Waxman litigation typically reflects a privately negotiated agreement governing when and on what terms the defendant may enter the market with a generic version.
At 607 days from filing to closure, the duration is consistent with a contested ANDA dispute that reached substantive negotiation before trial. The consent judgment structure means the specific commercial terms — including any licensed entry date — are not part of the public record. What remains unknown is whether Ascent received a royalty-bearing licence, an authorised-generic arrangement, or a straightforward date-certain market entry right. The earlier removal of Hetero Drugs suggests the two defendants may have pursued different litigation and commercial strategies.
Filing to Consent Judgment in 607 days
607 days — above the median for Hatch-Waxman ANDA cases resolved by consent judgment in Delaware
Consent judgment explained: what the resolution means for each party
Consent judgment is a court order, not merely a settlement agreement
A consent judgment differs from a private settlement: it is entered by the court and carries the force of a judicial order. In Hatch-Waxman cases, this mechanism is routinely used to formalise agreed market-entry terms, preserving the innovator’s ability to enforce the order if breached. Judge Hall’s signature on 8 May 2025 converts the parties’ agreement into an enforceable court decree, providing a stronger compliance mechanism than a contract alone.
Court-enforceable orderAstraZeneca preserves LOKELMA® patent without an invalidity finding
By resolving through a consent judgment rather than a contested merits ruling, ZS Pharma and AstraZeneca avoid any judicial finding on validity or non-infringement of US11738044B2. The patent remains intact and fully enforceable against any other party who did not participate in this action. This outcome is consistent with innovators managing generic entry timing while protecting patent assets for broader enforcement.
Patent survives unchallengedAscent gains defined market access without protracted trial risk
For Ascent Pharmaceuticals, a consent judgment typically delivers certainty: an agreed date or condition on which it may launch its ANDA product. This avoids the binary risk of a trial verdict. The specific entry terms are not public, but generic filers typically accept consent judgments only when commercial terms are commercially viable. Hetero Drugs, removed earlier via separate stipulation, had already resolved its position on different — and undisclosed — terms.
Negotiated entry termsHatch-Waxman consent judgments signal negotiated — not litigated — market structure
For the broader sodium zirconium cyclosilicate market, this resolution suggests AstraZeneca retained sufficient confidence in US11738044B2 to negotiate rather than litigate to judgment. Other potential ANDA filers for LOKELMA® should treat this patent as an active, unimpeached barrier. The consent judgment does not create collateral estoppel on validity — but the absence of any invalidity finding reinforces the patent’s litigation posture for future enforcement actions.
Active enforcement risk remainsFull party and counsel information
| Role | Name | Type | Detail |
|---|---|---|---|
| Plaintiff | ZS Pharma, Inc. | Company | Pharmaceutical innovator and AZ subsidiary — holder of US11738044B2 covering LOKELMA®Search in Eureka ↗ |
| Co-Plaintiff | Astrazeneca Pharmaceuticals, LP | Company | Search in Eureka ↗ |
| Defendant | Ascent Pharmaceuticals, Inc. | Company | Generic pharmaceutical manufacturer and ANDA filer — challenged LOKELMA® patent exclusivitySearch in Eureka ↗ |
| Co-Defendant | Hetero Drugs, Ltd. | Company | Search in Eureka ↗ |
| Plaintiff counsel | Alexandra M. Joyce | Attorney | Counsel for ZS Pharma, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Daniel M. Silver | Attorney | Counsel for ZS Pharma, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Gyuhyun (joanne) Bae | Attorney | Counsel for ZS Pharma, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Hassen Sayeed | Attorney | Counsel for ZS Pharma, Inc.Search in Eureka ↗ |
| Plaintiff counsel | James Yi Li | Attorney | Counsel for ZS Pharma, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Mark A. Hayden | Attorney | Counsel for ZS Pharma, Inc.Search in Eureka ↗ |
| Plaintiff law firm | McCarter & English LLP | Law Firm | Representing ZS Pharma, Inc.Search in Eureka ↗ |
| Defendant counsel | Kenneth Laurence Dorsney | Attorney | Counsel for Ascent Pharmaceuticals, Inc.Search in Eureka ↗ |
| Defendant counsel | Mark A. Hayden | Attorney | Counsel for Ascent Pharmaceuticals, Inc.Search in Eureka ↗ |
| Defendant law firm | Morris James LLP | Law Firm | Representing Ascent Pharmaceuticals, Inc.Search in Eureka ↗ |
| Presiding judge | Judge Jennifer L. Hall | Judge | Delaware District CourtSearch in Eureka ↗ |
Official order — verbatim text
The consent judgment entered by Judge Hall on 8 May 2025 resolves the infringement action without adjudicating the merits. In Hatch-Waxman practice, this phrasing signals that the parties reached agreement on market-entry terms, which the court formalised as an enforceable order. For AstraZeneca, this preserves US11738044B2 without compromise. For Ascent, it delivers defined commercial certainty. The substantive terms — including any royalty, authorised-generic right, or launch date — are not disclosed in the public docket.
US11738044B2 — sodium zirconium cyclosilicate oral suspension formulation
US11738044B2, filed under application number US16/415550, protects sodium zirconium cyclosilicate — a selective inorganic cation exchanger that captures potassium ions in the gastrointestinal tract. The patent covers the formulated oral suspension product LOKELMA® in both 5 g and 10 g per-packet presentations. This asset sits within AstraZeneca’s cardiovascular-renal portfolio, covering the active pharmaceutical ingredient and the formulation architecture that delivers the clinical dose. The patent’s grant provides protection extending well beyond the original NDA approval.
LOKELMA® competes in the hyperkalaemia management market alongside patiromer (Veltassa®), making formulation patents like US11738044B2 commercially critical barriers to generic entry. For competitors and ANDA filers, this patent — having survived two separate ANDA challenges without a validity ruling against it — represents a high-risk obstacle. The sodium zirconium cyclosilicate space is technically specialised, and the combination of API and formulation claims means designing around the patent is non-trivial. AstraZeneca’s willingness to litigate to consent judgment rather than licence early signals a strong confidence in the patent’s validity.
Should you run an FTO against US11738044B2 before entering the LOKELMA® market?
Any pharmaceutical company developing a sodium zirconium cyclosilicate oral suspension product — whether as an ANDA filer, authorised generic partner, or 505(b)(2) applicant — should treat US11738044B2 as a priority FTO target. The patent has survived two separate ANDA challenges in Delaware without an adverse validity finding. That track record, combined with AstraZeneca’s litigation resources, means market entry without a clear FTO or licence carries substantial infringement risk.
PatSnap Eureka’s FTO Search Agent can map the full claim scope of US11738044B2 against your proposed formulation, identify the prosecution history and any file wrapper estoppel, and surface related family members or continuation applications that may extend protection. Eureka also monitors the FDA Orange Book for new patent listings and litigation triggers, giving your R&D and regulatory teams an integrated view of the clearance landscape before you file an ANDA or initiate formulation development.
Run a freedom-to-operate analysis on US11738044B2 to assess your product’s exposure
Run FTO in Eureka →Similar Hatch-Waxman patent cases: sodium zirconium cyclosilicate and hyperkalaemia drugs
Explore related ANDA patent infringement cases in Delaware and other districts involving cardiovascular-renal API formulation patents similar to the LOKELMA® dispute.
What this case signals for the hyperkalaemia treatment IP landscape
The LOKELMA® consent judgment reflects a calculated patent strategy by AstraZeneca — and raises forward-looking questions for generic and competitor drug developers.
US11738044B2 remains valid and enforceable — no invalidity escape hatch created
Because the case ended by consent judgment, no court made findings on validity, obviousness, or non-infringement. Any new ANDA filer or competitor asserting sodium zirconium cyclosilicate formulations must confront this patent afresh. There is no precedent from this case to exploit.
Hetero’s early exit suggests bifurcated defendant strategies are viable
Hetero Drugs, Ltd. was removed by stipulation in October 2022 — over a year before this case was even filed. This signals co-defendants in multi-party ANDA litigation may resolve independently, and that early settlement by one defendant does not bind or assist later filers.
ZS v Ascent — key questions answered
The asserted patent is US11738044B2 (application number US16/415550), covering sodium zirconium cyclosilicate oral suspension formulations marketed as LOKELMA® 5 g and 10 g per packet. The patent was asserted by ZS Pharma, Inc. and AstraZeneca Pharmaceuticals, LP against Ascent Pharmaceuticals, Inc. and Hetero Drugs, Ltd. in the District of Delaware.
The case was resolved via a consent judgment entered by Judge Jennifer L. Hall on 8 May 2025. The case was formally closed on 18 June 2025. A consent judgment reflects a court-enforceable agreement between the parties, but the commercial terms — including any agreed market-entry date for Ascent’s ANDA product — are not disclosed in the public docket.
Hetero Drugs, Ltd. was removed from the related member case (No. 22-1099-JLH) via a stipulation so ordered by Judge Williams on 19 October 2022 — over a year before Case No. 1:23-cv-01188 was filed. The public record does not specify the commercial terms of Hetero’s resolution. This suggests Hetero and AstraZeneca reached a separate arrangement prior to the Ascent filing.
A consent judgment entered without a merits ruling does not create any finding on the validity, enforceability, or non-infringement of US11738044B2. The patent remains fully valid and enforceable against any third party not party to the consent judgment. This means future ANDA filers cannot rely on this case as precedent to challenge the patent’s validity.
The plaintiffs ZS Pharma and AstraZeneca were represented by McCarter & English LLP, with counsel including Daniel M. Silver, Alexandra M. Joyce, and Mark A. Hayden. The defendant Ascent Pharmaceuticals was represented by Morris James LLP, with Kenneth Laurence Dorsney as lead counsel. Notably, Mark A. Hayden appears in the docket for both plaintiff and defendant representations, which may reflect a conflict-check issue or a docketing anomaly.
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