The former head of sales for an Arizona drug company pleaded guilty Wednesday for his role in a conspiracy to defraud insurance companies by bribing doctors to prescribe a highly addictive fentanyl-based pain drug when it wasn't needed, according to federal prosecutors and court documents.

The man, Alec Burlakoff, 44, of West Palm Beach, Florida, is former vice president of sales for Insys Therapeutics Inc. of Chandler, Arizona. Court documents show that Burlakoff agreed to cooperate with prosecutors in their case against Insys at a hearing Wednesday in U.S. District Court in Boston.

Prosecutors said Burlakoff is the highest-level executive to admit wrongdoing in their investigation of the company's billionaire founder, John Kapoor, and five other co-defendants, all of whom have pleaded not guilty.