In the current state of Meridian Cloud, users get notified (per e-mail) when a document gets moved through the workflow. However, Meridian doesn't notify users when documents are put up for periodic review, or when the deadline for the periodic review is approaching. As per confirmation from support, there currently is no way to configure these type of periodic review notifications.
We think periodic review notifications would be a great quality of life improvement for reviewers.
As of now reviewers need to manually and regularly check if there are any periodic review documents with approaching deadlines.