Which of the following actions is NOT appropriate when an unanticipated problem arises in a clinical trial?

Withholding information from the subjects is not appropriate when an unanticipated problem arises in a clinical trial because ethical principles governing research require transparency and respect for participants' autonomy. Informed consent is foundational to ethical research practices; participants should be fully aware of any risks or changes that may affect their safety or the integrity of the study.

When an unanticipated problem occurs, it is essential to keep subjects informed so they can make informed decisions about their continued participation. This aligns with ethical guidelines and regulations that mandate communication with subjects regarding any issues that could impact their wellbeing and decision-making.

In contrast, revising the informed consent document and notifying the Institutional Review Board (IRB) are vital steps taken to ensure that the study remains compliant with ethical standards and regulations. Implementing protocol changes can help address future risks or issues identified through the unanticipated problem, enhancing the safety and integrity of the research for future participants.