West Virginia State Police said Dr. Robert Ferrante was picked up on Interstate 77 near Beckley, the Pittsburgh Post-Gazette reported. The Allegheny County District Attorney's Office issued a national alert after police officers who traveled to St. Augustine, Fla., to arrest him discovered he had departed.
Dr. Autumn Klein, 41, head of women's neurology at the University of Pittsburgh Medical Center, died in April. Investigators determined her collapse and her death three days later were caused by cyanide.
An affidavit of probable cause released Thursday said Klein told a friend she was planning to end her marriage and that Ferrante believed she was having an affair.
Ferrante, 64, a neuroscientist at the university, was being held in West Virginia pending extradition proceedings.
"He's adamant he had nothing to do with her death and plans to fully defend himself," his attorney, William Difenderfer, said.
The couple's daughter was placed in the custody of her maternal grandparents.