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Acetaminophen Falsely Raises Glucose Sensor Readings by Wide Margin

Acetaminophen falsely elevates continuous glucose monitor (CGM) readings by a large margin, according to a new report that quantifies and raises cautions about the phenomenon as the devices are used increasingly by patients.

The results of an analysis conducted with 40 type 1 diabetes patients were published online August 12, 2015 in Diabetes Care by David M Maahs, MD, associate professor of pediatrics at the Barbara Davis Center for Childhood Diabetes, University of Colorado, Denver, and colleagues.

In the current study, CGM readings were as much as two- to nearly fourfold higher than finger-stick readings following ingestion of acetaminophen.

User guides for currently licensed CGM devices made by Dexcom and Medtronic Minimed include a warning about acetaminophen interference with the devices. Moreover, since the CGM devices aren't approved by the US Food and Drug Administration for use in making treatment decisions, the product guides also advise patients to instead base insulin dose calculations on finger-stick blood glucose monitor results.

The degree to which the instructions are heeded isn't known. Few published studies have documented the magnitude of the acetaminophen effect, particularly on newer sensors. The rapid development of closed-loop technology, which uses CGM readings to automate insulin delivery, also makes this a concern, the authors say.

"It's very important that the effect of acetaminophen on CGM — and its magnitude — be known, especially as CGM technology is being used increasingly by patients. Also, with artificial-pancreas technology rapidly advancing and with the potential for insulin dosing based on CGM instead of only with meter glucose, this is an important topic," Dr Maahs told Medscape Medical News.

The 40 subjects had a mean age 28.5 years and HbA1c 7.3%. They all used the Dexcom system.

After taking 1000 mg of acetaminophen, the subjects performed finger-stick blood glucose checks at 30 minutes and 1, 2, 4, 6, and 8 hours. There were significant differences between the CGM and meter readings (P < .01) for the entire 8-hour period. The greatest mean difference was 61 mg/dL, occurring at 2 hours, but there was a wide range of individual variation.

Three patients had blood glucose meter values less than 70 mg/dL with much higher CGM readings — 63 vs 138 mg/dL, 46 vs 175 mg/dL, and 51 vs 184 mg/dL. In 10 patients, the CGM values read higher than 180 mg/dL, but the meter reading was over 100 mg/dL lower.

"We need to better understand why the effect varies," Dr Maahs noted.

The differences between CGM and meter weren't affected by age, body mass index, HbA1c, or the number of boluses for food ingestion, but the effect was greater in women (P = .04).

The phenomenon would be expected to affect the CGM's reporting of blood glucose trends as well as individual readings. "The impact of acetaminophen is greatest at approximately 2 hours, with a diminishing effect over 8 hours, so acetaminophen could have an effect on glycemic trends as its effect peaks and wanes,"

Newer technology is being developed to further limit or eliminate this effect. "Until those technologies are available, this is an important issue for patients and clinicians to be aware of," he said, adding, "This should not discourage CGM use but rather inform and educate people. In fact, our study group is an advocate of CGM use for people with type 1 diabetes."
Source: Medscape Medical News 2015
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