I think finding some type of verbal evaluation
( without off course allowing the active students to overshadow the passive students) mid way through the lecture may be a good way to make sure that the students are re-engaged and re-focused.
I haven't had the challenge of needing to keep students refocused in a class that I thought recently as most of the adult students have enjoyed sharing their work experiences that pertain to the topic that is being covered with the class.
