Requested WoW macro

Is it possible to make a macro to interrupt the focus target only if it’s casting, or only casting a specific spell?

Reason I ask is we’re working on Heroic Protectors. While attacking Kaolan, Regail casts Lightening Bolt and Asani casts Water Bolt. Asani’s Water Bolt must be interrupted but one of our three on interrupt duty keeps hitting his interrupt focus target macro when he sees Regail begin casting Lightening Bolt and then it’s on CD for Regail’s Water Bolt.