Final answer:
The appropriate initial action is to report the situation to the nurse manager.
Step-by-step explanation:
The appropriate initial action when a nurse suspects another nurse of signing for a wasted narcotic without witness and engaging in a pattern of behavior is to report this immediately to the nurse manager.
This action is important because it ensures that the proper authorities are aware of the situation and can take appropriate action to address the issue.
Signing the narcotic sheet and documenting the event in an incident report is not the appropriate initial action in this case, as it does not address the issue directly. Confronting the nurse about the suspected drug use or counseling the colleague about risky behaviors should also be done, but it is not the first step to be taken.