Maddox developed the immediate-release hydrocodone/paracetamol drug Lortab, aiming to fill a gap in the market between over-the-counter pain relievers and the strongest pain drugs. He initially focused on oncology and post-operative patients, but found a broader reach in dental procedures. He incorporated his company as the drug's sole distributor in 1984.
Maddox sold his company in 1989. In 1992 he launched Diagnostic Health, a chain of imagine centers, which was acquired by HealthSouth. He was hired as president and chief operating officer of what became the company's diagnostics division. It was spun off in 2007 to become the Diagnostic Health Corporation.
Maddox and his wife, Susan, had three children: Russell Jr, Kelley and Leigh Ann. She died in 2018.