Marcus,
I hope this finds you well. I am writing in connection with our ongoing engagement (Ref. No. 1037-00002, dated April 22, 2025) on behalf of Solstice Biomedical Inc. concerning the FDA regulatory strategy for the Solstice Lumina™ Continuous Glucose Monitoring System, comprising the Lumina C14 implantable sensor and the Lumina R7 wearable reader/transmitter (product code QKQ, 21 C.F.R. § 862.1355, Class II).
The purpose of this email is to communicate Calderwood & Harkness's assessment of the regulatory timeline for U.S. 510(k) clearance, following a thorough review by our Healthcare & Life Sciences team of the submission pathway, clinical data requirements, and current FDA review timelines at the Center for Devices and Radiological Health (CDRH). As you know, the initial aspiration communicated by Solstice management was to achieve FDA clearance by Q1 2026 — that is, by the end of March 2026. After careful analysis, we have concluded that this target requires revision, and I want to lay out our reasoning candidly so that the team can plan accordingly.
**Assessment of the Original Q1 2026 Target**
To be direct: our team has concluded that the Q1 2026 clearance target is aggressive and is not achievable under the current regulatory plan without introducing unacceptable risk to the quality and completeness of the submission. I want to emphasize that this conclusion does not reflect any deficiency on Solstice's part — the team has been responsive and well-organized throughout this engagement. Rather, the timeline constraint is driven by the inherent sequencing of required regulatory steps and by FDA's own review timelines, neither of which can be meaningfully compressed.
**Key Factors Driving the Revised Timeline**
The following factors, taken together, make the Q1 2026 target impracticable:
**(a) Pre-Submission (Q-Sub) Meeting Process**
The Pre-Submission meeting request is targeted for submission to FDA (CDRH, Office of Health Technology 2 — Division of Chemistry and Toxicology Devices) by June 2, 2025. The Pre-Sub meeting package, which must be submitted at least 60 days in advance of the meeting itself, is targeted for submission by June 16, 2025. FDA typically schedules Pre-Sub meetings within 75 days of receiving the meeting request; accordingly, our targeted meeting date is August 14, 2025.
FDA's written feedback following the Pre-Sub meeting is essential before we can finalize the clinical study protocol and the 510(k) submission strategy. This is particularly important here because any FDA requests for additional data — or any questions regarding the predicate device approach — would require additional lead time. As you know, our submission strategy relies on a primary predicate of the NovaSense GlucoTrack NX-500 (K211034, cleared June 18, 2022) and a secondary predicate of the NovaSense GlucoTrack NX-700 (K230489, cleared March 7, 2024). While we believe this predicate selection is well-supported, the Pre-Sub is the appropriate vehicle for confirming FDA's alignment, and any course corrections coming out of that meeting must be built into the plan.
**(b) Biocompatibility Testing Timeline**
Biocompatibility testing commenced at Whitmore Laboratories Inc. on March 3, 2025, and covers an extensive scope under ISO 10993. For the C14 implantable sensor, the testing program includes cytotoxicity, sensitization, irritation, acute systemic toxicity, subchronic toxicity, implantation, hemocompatibility, and genotoxicity. For the R7 wearable reader, the program covers cytotoxicity, sensitization, and irritation.
The target completion date is August 31, 2025. The subchronic toxicity and implantation studies alone require extended exposure periods that are dictated by the standard and cannot be compressed without compromising the scientific integrity — and therefore the regulatory acceptability — of the results.
**(c) Clinical Study Duration — LUMINA-US (Protocol SBD-LUM-CL-001)**
The pivotal clinical study, LUMINA-US, is designed as a prospective, single-arm, multicenter study enrolling 350 subjects (175 with Type 1 diabetes and 175 with Type 2 diabetes) across 6 U.S. clinical sites, to be conducted by Veltrano Clinical Research Organization Inc. The study cannot commence until all of the following conditions are satisfied:
(i) Pre-Sub feedback is received from FDA and the study protocol is finalized; (ii) IRB approval is obtained from Clearwater Institutional Review Board LLC (IRB Registration No. IRB-2019-04821); and (iii) IDE exemption status under 21 C.F.R. § 812.2(c)(3) for non-significant risk diagnostic devices is confirmed, either through the Pre-Sub process or independently.
Given these dependencies, the planned study commencement date is September 15, 2025. The estimated study duration is approximately 6 months, reflecting 14 weeks of enrollment, a 14-day sensor wear period, and approximately 8 weeks for data analysis, data lock, and preparation of the final clinical study report. This yields a planned study completion date of March 15, 2026.
The critical point is this: even assuming the clinical study starts precisely on schedule in September 2025, data lock and the final clinical study report would not be available until mid-March 2026 at the earliest. This alone leaves no time whatsoever for 510(k) preparation, submission, and FDA review before the end of Q1 2026.
**(d) 510(k) Submission Preparation**
Following clinical study completion on or about March 15, 2026, the team will require approximately 6 weeks to finalize the 510(k) submission package. This is a traditional 510(k) submission covering both the C14 sensor and the R7 reader/transmitter as a system, which adds complexity. The submission must incorporate clinical data, performance testing results, software documentation (including Firmware v3.4.2, Reader OS v2.1.0, LuminaPredict Algorithm v2.1, and Mobile App v1.0.3), cybersecurity documentation, and labeling.
Our target 510(k) submission date is April 30, 2026. For budgeting purposes, the applicable FY2025 510(k) standard review user fee is $22,417. We have confirmed that Solstice Biomedical Inc. does not qualify for the MDUFA small business fee reduction, as the consolidated global parent revenue of approximately €187.4 million (approximately $204.3 million at €1 = $1.09) exceeds the applicable threshold.
**(e) FDA Review Timeline**
The statutory review period for a traditional 510(k) is 90 calendar days. However, in practice, CDRH review of CGM devices — particularly those incorporating new sensor technologies, novel predictive algorithms, and cybersecurity considerations — has been running closer to 120 to 150 days when additional information (AI) requests are factored in. Assuming submission on April 30, 2026, a 90-day base review period would bring clearance no earlier than late July 2026. Accounting for a likely AI request and the associated response cycle, a realistic clearance target is Q3 2026.
**Revised Timeline Summary**
Based on the foregoing, we recommend the following revised milestone timeline:
| Milestone
**Mitigating Considerations**
While I recognize that the revised timeline is later than originally hoped, there are several factors that give us confidence in the overall strength of the submission and Solstice's competitive position:
First, the Lumina CGM System's existing EU MDR CE certification (Certificate No. MCA-2024-07319, issued September 12, 2024, by Meridian Conformity Assessment GmbH, Notified Body 0483) and the system's commercial launch in the EU since September 2024 provide a strong foundation of clinical and technical data, much of which can be leveraged for the FDA submission. This is a meaningful advantage that many first-time applicants do not have.
Second, Solstice's prior FDA clearance history — specifically the GlucoStrip RX-200 (K192847, cleared November 14, 2019) — demonstrates institutional familiarity with the 510(k) process and an established relationship with CDRH, both of which should facilitate a constructive Pre-Sub interaction and a smoother review.
Third, Pinnacle Regulatory Consulting Group LLC, which has been engaged since January 15, 2025, is actively preparing the technical summaries and performance testing protocols. Their work is proceeding on track and will help maintain the schedule on the submission preparation side.
Finally, the revised Q3 2026 clearance target remains a competitive timeline for a CGM device incorporating novel sensor technology and a new predictive algorithm, and it positions Solstice well for a Q4 2026 U.S. commercial launch.
**Recommendation and Next Steps**
We recommend that Solstice adopt the revised timeline as the baseline for internal planning and resource allocation. We also suggest that you and Niamh brief Dr. Eoin Gallagher and Dr. Aisling Burke on the revised timeline at your earliest convenience so that expectations are aligned across the leadership team.
We would welcome the opportunity to schedule a call with you, Dr. Tierney, and the C&H team to walk through the revised timeline in detail and address any questions. Amy Whitfield will follow up to coordinate scheduling.
In the coming days, we will also circulate a detailed Regulatory Timeline and Milestone Tracker that we are currently preparing, which will identify all dependencies, critical path items, and key decision points.
Separately, I want to note that our team is coordinating with Crestline IP Advisory LLC on the ongoing freedom-to-operate analysis related to the NovaSense patent portfolio. This workstream does not impact the regulatory timeline but remains an important parallel effort, and we will keep you apprised of developments there as well.
Marcus, I want to close by expressing our confidence in the overall regulatory strategy and in the strength of the Lumina CGM System's substantial equivalence argument. The predicate framework is sound, the clinical program is well-designed, and the technical file is being assembled with care. The revised timeline is the responsible path to a successful clearance, and we are committed to executing against it with the same rigor we have brought to the engagement from the outset.
Please do not hesitate to reach out if you have any questions or would like to discuss further. I am available at your convenience.
Best regards,
Miriam Calloway Partner, Healthcare & Life Sciences Calderwood & Harkness LLP 1401 K Street NW, Suite 900 Washington, D.C. 20005 (202) 555-8140