Breast implants, metal-on-metal total hip replacement devices and nitinol in devices such as the Essure permanent birth control device are among the products FDA Commissioner Scott Gottlieb and device center chief Jeff Shuren called out in a statement.

The agency also released interim results from postmarket surveillance studies for metal-on-metal total hip replacement devices.

The implants, sold in the past by companies including Johnson & Johnson, have been dogged by safety concerns in recent years, leading the FDA to move the devices into a higher risk category in 2016. The agency also banned marketing of the devices before approval under the tighter standards. 

While there are no such approved devices for the U.S. market currently, FDA says the findings will inform how new metal-on-metal devices submitted for review are evaluated.

Patients with a metal-on-metal total hip replacement device implanted have shown "significantly higher blood levels of metal ions" than those without metal implants.

"While that’s not unanticipated, the data also suggest that the standard blood level threshold measurement of 7.0 parts per billion (micrograms/liter) or higher for metal ions, is not optimal to determine if an implant is functioning safely," Gottlieb and Shuren said.

Severe symptoms were present in some patients with lower levels of metal ions in their blood, while certain patients had higher levels and no adverse events. Patients who had the device removed had higher levels of metal ions in their blood than those that still had the implant in their body, according to FDA.

"This suggests that there are additional factors, besides metal ion levels, that affect which patients experience adverse events from metal-on-metal total hip replacement devices," Shuren and Gottlieb said.

FDA emphasized for the vast majority of patients, the benefits of metal devices "continue to outweigh their risks."

"However, for certain small subsets of patients who exhibit sensitivities to select materials, we must determine what additional actions we should take to make sure they are protected and understand the unique risks they may encounter," Gottlieb and Shuren said in a statement.

In June 2016, the agency finalized guidance outlining expectations for biocompatibility evaluations of materials. And it is working to stand up the National Evaluation System for health Technology (NEST) to better monitor devices in real world settings.

"Based on our evaluation and discussions with experts elsewhere in the government and academia, we believe the current evidence, although limited, suggests some individuals may be predisposed to develop an immune/inflammatory reaction when exposed to select materials," Gottlieb and Shuren said.

The regulators said current efforts to predict adverse events, such as skin patch testing, may be inadequate due to non-allergenic responses. Further material science study and the development of novel screening tests may lead to patients not being implanted with devices that contain materials to which they are hypersensitive, they added.

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