Johnson & Johnson is required to add new warnings to its diabetes drug, Invokana, about the risk of foot and leg amputations, the U.S. Food and Drug Administration said on Tuesday.

Final results from two clinical trials showed leg and foot amputations occurred about twice as often in patients with type 2 diabetes treated with Invokana, known also as canagliflozin, as those given a placebo, the FDA said in an announcement posted on its website.

The warnings include a boxed warning, reserved for the most serious possible adverse events, the FDA said.

Invokana belongs to a relatively new class of type 2 diabetes drugs called SGLT-2 inhibitors, which help remove excess blood sugar through urine. Others in the class include Eli Lilly and Co's Jardiance and AstraZeneca Plc's Farxiga.

The FDA noted that results of one clinical trial showed that over the course of a year the risk of amputation in patients treated with Invokana was equivalent to 5.9 out of 1,000, compared with 2.8 out of 1,000 for patients given a placebo.

A second trial showed the risk of amputation was equivalent to 7.5 out of every 1,000 patients treated with Invokana compared with 4.2 out of every 1,000 patients given a placebo.

The agency said amputations of the toe and middle of the foot were the most common but that amputations involving the leg, below and above the knee, also occurred.

Untreated type 2 diabetes can cause blindness, nerve and kidney damage and heart disease.