Amputation is a serious concern for people with diabetes. Some patients are at an increased risk if they are taking the popular type 2 diabetes medication Invokana, according to a 2017 Food and Drug Administration (FDA) Drug Safety Communication.

The drug advisory warned that patients taking Invokana had approximately a two-fold risk of amputation, most often affecting the toe and middle of the foot, compared to patients taking a placebo. As a result, the FDA required its strongest warning – a boxed warning – be added to the labels of Invokana.

According to data from two large clinical trials, the risk of amputation over a year’s time in one study was equivalent to 5.9 out of every 1,000 patients treated with Invokana compared to just 2.8 out of every 1,000 patients treated with placebo. A second study found that over a year’s time, 7.5 out of every 1,000 patients treated with Invokana required amputations compared to just 4.2 out of every 1,000 patients treated with a placebo.

Most amputations reported in the studies were of the toe and middle of the foot, but some involved the leg, as well as below and above the knee. Some patients had more than one amputation, and some involved both limbs.

Complications with diabetes

People with diabetes are already prone to complications such as nerve damage, poor circulation and peripheral artery disease (PAD), which can increase the risk of ulcers and infections that can lead to amputation. As a result, they are 28 times more likely to have a limb amputated compared to people without the chronic disease, accounting for 60 percent of all non-traumatic amputations performed in the United States, according to the diabetes resource website TheDiabetesCouncil and the Centers for Disease Control and Prevention (CDC), respectively. Most amputations due to diabetes are performed on the lower extremities, such as the toes, feet and legs. Some diabetics require amputations below the knee.

The most common precipitating medical events leading to the need for amputation in diabetics include lower limb infections, gangrene, diabetic foot ulcers and ischemia (inadequate blood supply to a part of the body).

Invokana was approved by the FDA in March 2013. It contains the active drug ingredient canagliflozin and was first licensed from Mitsubishi Tanabe Pharma Corporation and later to Johnson & Johnson’s unit Janssen Pharmaceuticals for worldwide distribution.

Canagliflozin is sold as a single ingredient medication under the brand name Invokana, and in combination with metformin under the brand name Invokamet, which also comes in an extended-release formula called Invokamet XR. These medications are in a class of drugs known as sodium-glucose cotransporter-2 inhibitors, or SGLT2 inhibitors.

How does Invokana work?

Invokana lowers blood sugar in patients by working through the kidneys to allow excess sugar to be excreted through the urine. This mechanism, however, may be the cause of some Invokana side effects.

For example, in 2015, the FDA warned that Invokana and other drugs containing canagliflozin were linked to urinary tract infections that could become dangerous if the infections spread to the kidney. A year later, the agency issued another warning regarding an increased risk of kidney injury in Invokana users, and recommended health care professionals evaluate kidney health of patients before prescribing the medication.

Invokana’s effect on the kidneys may also be to blame for the increased risk of lower limb amputations. Dr. J. Michael Gonzalez-Campoy, MD, PhD, FACE, medical director and CEO of the Minnesota Center for Obesity, Metabolism and Endocrinology speculated to EndocrineWeb that because Invokana works through the kidneys, someone taking the drug “may get dehydrated, possibly triggering constriction of the blood vessels in the limbs and reduced blood flow there. If blood flow decreases and foot ulcers occur, a serious bacterial infection may take hold, requiring amputation.”

Whatever the cause, the risk cannot be ignored. The FDA urges patients taking Invokana, Invokamet or Invokamet XR to contact their health care provider immediately if they notice new pain or tenderness, sores, ulcers, or infections in the legs or feet.

If you or a loved one has suffered an amputation after taking Invokana, you may be entitled to compensation for medical expenses, lost wages, and pain and suffering. We at Beasley Allen Law Firm have helped thousands of clients get the justice they desperately want and deserve. If you feel you have a case, or just have questions, contact us for a free consultation.

FDA Drug Safety Communication
American Diabetes Association
FDA Invokana Safety Label
Drug Development Technology

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