(Reuters) - An Alabama doctor was sentenced on Thursday to 20 years in prison after being convicted with a colleague of prescribing painkillers through two clinics for no legitimate purpose, in a case tied to the U.S. probe of Insys Therapeutics Inc.

John Couch, who with Xiulu Ruan ran the Physicians Pain Specialists of Alabama clinics, was sentenced by U.S. District Judge Callie Granade in Mobile, Alabama, after a jury in March found them guilty of racketeering conspiracy and other felonies.

Ruan is scheduled to be sentenced on Friday. Brandon Essig, a lawyer for Couch, confirmed Thursday’s sentence and said he planned to appeal.

“We don’t think there was sufficient evidence in the case,” he said.

According to court papers, Physician’s Pain Specialists of Alabama had two clinic locations in Mobile.

Prosecutors said through those clinics, Couch and Ruan, motivated by their own financial self-interest, regularly wrote prescriptions for large quantities of addictive medications including fentanyl without a legitimate medical purpose.

The case, filed in 2015, focused partly on two brand name instant-release fentanyl drugs, Subsys, manufactured by Insys, and Abstral, which was then manufactured by Galena Biopharma Inc.

According to prosecutors, while both drugs were approved by the U.S. Food and Drug Administration for cancer pain, Ruan and Couch prescribed Subsys and Abstral for off-label uses to treat neck, back and joint pain.

Prosecutors said the doctors received illegal kickbacks from Insys in exchange for prescribing Subsys and became among the top U.S. prescribers of the drug.

Couch and Ruan also bought $1.6 million of Galena shares and tried to manipulate its stock price by driving up sales of Abstral, prosecutors said.

In December, federal prosecutors in Boston announced charges against several former Insys executives and managers, including former CEO Michael Babich, in connection with a scheme to bribe doctors to prescribe Subsys. They have pleaded not guilty.

Federal charges have also been filed in four states against at least five other ex-Insys employees. Insys earlier this month said that it was working to settle the U.S. Justice Department probe.

Galena, which divested of Abstral in 2015, earlier this month said it had tentatively agreed to pay $7.5 million to resolve a U.S. investigation into its marketing and promotional practices for Abstral.

The case is U.S. v. Couch, et al, U.S. District Court, Southern District of Alabama, No. 15-cr-88.