Implantable Long-Term CGM Solutions

Implantable Long-Term CGM Solutions

An implantable continuous glucose monitor (CGM) puts the whole sensor under the skin instead of on a filament attached to a wearable patch. Senseonics' Eversense 365, cleared by FDA in September 2024, is labeled for up to 1 year of wear in adults 18 and older [1]. When FDA reviewed the Eversense design in 2024, it noted that other CGMs approved for treatment decisions last 7 to 15 days [2]. The trade-off is a clinic visit. A healthcare provider inserts the sensor and later removes it, and the system still asks for fingerstick calibrations [1].

How the implanted sensor works

The sensor is tiny, about 3.5 mm by 18.3 mm, and it measures glucose with light rather than an enzyme reaction. A fluorescent indicator on its surface binds glucose reversibly and glows brighter as more glucose binds [1]. The sensor has no battery. A smart transmitter worn on the skin above it powers it by radio frequency, converts the signal to a glucose value, and sends a reading to a phone app every 5 minutes; the transmitter needs charging every day [1]. Our Eversense fluorescence explainer covers the optics.

Here's the detail that surprised us: the sensor carries a drug. A silicone collar slowly releases 1.75 mg of dexamethasone acetate, a corticosteroid, to damp the body's foreign body reaction around the implant [1]. FDA's review credits that steroid with keeping the sensor working for months, so it needs replacing less often [2].

From 90 days to a full year

FDA approved the first Eversense system in June 2018 for up to 90 days [3]. The Eversense E3 followed in February 2022 with a redesigned sensor rated for up to 180 days [4]. In April 2024, FDA granted a De Novo request for the Eversense AP, a 6-month version built to feed readings to automated insulin delivery systems, and created a device category for integrated CGMs whose sensors contain dexamethasone [2]. The Eversense 365 was cleared that September with the AP as its predicate [1]. The E3 is the older generation, though as of March 2026 Senseonics still listed it alongside the 365 [5].

Insertion and removal

A trained provider places the sensor under the skin of the upper arm through a small incision, which Senseonics says is usually closed with adhesive strips rather than stitches [6]. The outer upper arm is the only insertion site, and removal is a clinic procedure too [2].

FDA spelled out the procedure risks plainly. They include pain, inflammation and infection, a sensor that breaks and leaves a fragment under the skin, trouble getting the sensor out, and scar tissue from repeated procedures in the same area [2]. FDA's answer is required training for the providers who do the procedures, plus warnings in the labeling [2].

The best real-world numbers we found come from a registry of earlier 90-day and 180-day sensors in Europe and South Africa. It enrolled 3,023 people who had 5,417 sensors inserted between 2016 and 2018, and it reported no serious adverse events related to the device or the procedure [7]. The most common related problems were infection at the sensor site (0.96%, or 2.46 events per 100 patient-years), a sensor that couldn't be removed on the first attempt (0.76%), and irritation under the transmitter's adhesive patch (0.66%) [7]. Those sensors predate the 365, so the figures say more about the procedure than the current sensor.

Because the transmitter sits on adhesive over the sensor, it can come off for a shower and go back on without wasting a sensor. No glucose data is recorded while it's off [6] [8].

Calibration hasn't gone away

The Eversense 365 is approved to replace fingersticks for diabetes treatment decisions, yet it still uses fingerstick readings to calibrate [1]. After a 24-hour warm-up, it asks for 4 calibrations spaced 2 to 12 hours apart, all within 36 hours. Then it asks for one a day through day 13. From day 14 on, it asks once a week [1]. That weekly phase is the real change from the E3, which Senseonics describes as needing a calibration every day after day 21 [5].

Accuracy across a year of wear

In the ENHANCE study behind the clearance, 110 adults at 4 US sites wore the sensor, and their readings were checked against a laboratory glucose analyzer at clinic visits through day 365 [1]. Across the year, 92.0% of sensor readings landed within 20% of the lab value. MARD (mean absolute relative difference, the average gap between sensor and lab readings) stayed between 7.8% and 9.9% in every 30-day stretch [1]. Of the 96 participants still enrolled at day 365, 86 still had a working sensor, which FDA's summary records as 90% survival [1]. Our MARD comparison explains why cross-brand comparisons are tricky.

What the labeling warns about

The transmitter is MR Unsafe and must be removed before an MRI scan, and the system is contraindicated for people who can't take dexamethasone [1]. Two kinds of drugs interfere with readings. Tetracycline-class antibiotics, such as doxycycline, can falsely lower them, and FDA's summary says readings shouldn't be relied on while taking those drugs. Mannitol or sorbitol given intravenously, or in irrigation or peritoneal dialysis solutions, can falsely raise them; the sorbitol in ordinary food doesn't [1].

The system also wasn't tested in some groups, including people who are pregnant or nursing, anyone under 18, and people with another active implanted device such as a defibrillator [1]. Whether any of these warnings rules the device out for a particular person is a question for that person's care team.

Working with automated insulin delivery

The Eversense 365 is an iCGM, short for integrated CGM, so its labeling allows it to send readings to connected devices, including automated insulin delivery (AID) systems [1]. The first pairing on the market is the twiist AID System from Sequel Med Tech. Senseonics reported launching the combination across the US by March 2026 and said it planned to add more AID partners during 2026 [5].

According to twiist, its system uses the CGM's readings and predicted glucose levels to adjust insulin delivery, and it is meant for people with type 1 diabetes ages 6 and up [8]. Because the Eversense 365 is labeled only for adults, the pairing applies to adults with type 1 diabetes [1] [8]. More on how CGMs and pumps connect is in our AID interoperability article.

Coverage and access

Senseonics says the Eversense 365 is covered by most commercial health plans and by Medicare. For Medicare, it notes that a prescription is required, the patient must meet Medicare's eligibility criteria, and coinsurance and deductibles can apply [6]. Those are the company's statements, so a plan's own coverage documents are the final word. The procedures carry their own costs, too: Senseonics' savings offer for commercially insured patients doesn't apply to insertion or removal [6].

Senseonics took US sales back from Ascensia Diabetes Care on January 1, 2026. It also reported that its Eon Care inserter network had grown to 60 providers, who performed about 24% of US insertions in 2025 [5].

What's still in development

Senseonics received FDA approval for an investigational device exemption (IDE) to run a pivotal trial of Gemini, a sensor with its own battery, and as of March 2026 expected to finish that trial in the second half of the year. Gemini is investigational and not sold [5].