Following a spate of product recalls and patient injuries, the Food and Drug Administration is advising doctors to use extra care when putting medical-grade wires and tubes into complex blood vessels in the heart, legs and brain.

The concern centers on the slippery coatings applied to narrow medical devices used inside blood vessels, including "lubricious" friction-reducing coatings made by Twin Cities companies that are used in millions of minimally invasive procedures. The FDA issued a special safety letter Nov. 23 after examining 11 product recalls and 500 adverse event reports that included nine deaths.

The coatings are supposed to make it easier for a doctor to safely feed a wire or tube through blood vessels. But the FDA said particles from these "hydrophilic" coatings can flake off and potentially obstruct blood flow.

The FDA's safety letter follows last month's publication of a report from its MedSun program, which surveyed health care providers and found the devices generally get high marks: "For those who use hydrophilic-coated devices frequently, they believe that the lubricity of devices is essential to maneuvering in patients with narrow blood vessels or those with difficult anatomy."

Companies sold more than $6 billion worth of coatings in 2013, and sales are expected to climb to $9 billion by 2019 according to one analysis last year, by BCC Research.

At least two Twin Cities companies make the coatings, including SurModics and Harland Medical Systems, both of which are in Eden Prairie. Publicly traded SurModics, which earned about half its $57 million in revenue last year from various hyrdophilic coatings, declined to comment.

Harland spokesman Drew Summerville said none of his company's customers have complained about the specific issue outlined by the FDA. Harland is a private company and doesn't reveal its finances.

At least six other companies around the U.S. make the coatings. Many sell the coatings to larger device makers that put them on their interventional guide wires and catheters, including Boston Scientific Corp., Medtronic and St. Jude Medical.

"The FDA has not concluded that any specific manufacturer or brand of these devices is associated with higher risks than others," the FDA's letter this week says.

Interventional radiology has revolutionized many medical procedures by allowing doctors to see inside the body as they guide very thin tools and devices to their targets, turning blood vessels into a system of vascular highways to reach diseased organs or clogged arteries.

Doctors can thread surgical balloons into clogged arteries in the legs, unfurl stents in diseased vessels near the heart and deploy tiny metal nets in the brain to catch stroke-causing particles. The technique avoids large incisions by entering through a puncture in a major vessel, but it relies on doctors' ability to maneuver guide wires and tubes around tight corners. That makes slipperiness a positive attribute.

Examinations of 11 product recalls since 2010 and 500 adverse-event reports since 2014 have turned up evidence that the slippery coatings can flake off and lead to health problems, including narrowing or blocking of blood vessels in the heart, lungs and brain. Nine people in the literature died after particles from devices used in the heart and brain flaked off in the body and contributed to heart attack and brain bleeding, the FDA said.

Many factors are believed to lead to the flaking. They include difficult patient anatomy, physicians' procedural techniques, use of the wrong device, incorrect preoperative device prep in the hospital, improper storage conditions and issues in the device design and manufacturing process, the FDA said.

"The FDA believes the overall benefits of these devices continue to outweigh the risks. However, health care providers should be aware of potential problems and consider certain actions before use," agency officials wrote.

Those recommendations include selecting the right device, because wires and catheter tubes for the legs might have different performance requirements than those used in the brain. The FDA also said hospitals should follow manufacturers' recommendations for storage conditions, and doctors should adhere to rules on proper preoperative soaking of devices. The full recommendations list is at

Joe Carlson • 612-673-4779

Twitter: @_JoeCarlson