Medtronic is upping the ante in patent dispute with competitor Axonics Inc. that has already lasted more than four years.

The dispute centers on Medtronic's InterStim device, an implanted neurostuimulator used to treat patients with an overactive bladder and bowel-control conditions. On Thursday, Medtronic filed a complaint with the U.S. International Trade Commission (ITC) and a related lawsuit in the U.S. District Court for the District of Delaware in an effort to block Axonics from importing or selling certain products that it alleges infringe on Medtronic patents.

"Medtronic is continuing our efforts to stop Axonics from profiting off of their unauthorized use of our innovations and intellectual property," said Mira Sahney, president of the pelvic health business in the neuroscience portfolio at Medtronic, in a statement.

The action marks the first time Medtronic has ever filed an ITC complaint. The ITC investigates cases of import injury and U.S. intellectual property rights violations.

Axonics received approval for a device similar to InterStim in 2019, prompting Medtronic to charge the smaller company with patent infringement. Medtronic first sued Axonics in November 2019 in the U.S. District Court for the Central District of California. That case remains pending.

"We believe the allegations of the Medtronic affiliates are without merit," said Axonics in its annual financial report filed Thursday. The company also indicated the legal battle could still last for an "extended period of time."

Axonics has challenged the validity of some Medtronic patents. In July, the U.S. Court of Appeals for the Federal Circuit found the U.S. Patent Office's Patent Trial and Appeal Board (PTAB) had incorrectly analyzed the case. That postponed a jury trial scheduled for August 2023 in the California case, which can't move forward without further decisions from the PTAB.

Medtronic's new lawsuit raised competitive issues: "Axonics has hired a U.S. sales team that includes former members of Medtronic's sales team who received training from Medtronic."

California-based Axonics reported sales of $366.4 million last year, a small fraction of the scale of Medtronic's business. In January, Boston Scientific Corp. announced it would acquire Axonics in a $3.7 billion deal, expected to close in the first half of this year.

A Boston Scientific spokeswoman declined to comment and said the company and Axonics will continue to operate as separate companies until the transaction closes.