He has made four Amlin Cup appearances, the Dragons completing their group games this season against London Wasps at Rodney Parade on Thursday night.
Wales interim head coach Rob Howley announced that Coombs will be joined by Cardiff Blues back row forwards Josh Navidi and Andries Pretorius, second row James King (Ospreys) and Ospreys wing Eli Walker.
Pretorius, the 27-year-old Blues captain, was born in Nelspruit, South Africa, and qualifies on residency.
"We have put together a very experienced squad and complimented that by rewarding the in-form players with a call-up," said Howley.
"The players in the squad have been playing really well and we have been pleased with their individual performances.
"We have a group of players who know how to win big matches and have experienced success. We are adding to that, players who have stood out and performed well for the regions this season."
The 2012 Grand Slam Champions begin the defence of their title against Ireland at the Millennium Stadium on Saturday, 2 February, before facing France in Paris the following weekend.