Pythro V was the inhabited fifth planet in its star system. This was the homeworld of the Pythrons.
Con artist Martus Mazur defrauded an elderly couple from this planet in 2370, for which they pressed charges against him. (DS9: "Rivals")
This planet was only mentioned in dialogue.
According to the script, the pronunciation for Pythro was "PIE-throw". 
According to StarTrek.com, this planet orbited
Pythro in the populated Federation/Bajoran space. The planet had cooperative legal treaties with Bajor