Formal approaches to safety monitoring of clinical trials in life-threatening conditions

Large clinical trials in life-threatening conditions are usually conducted under the surveillance of a Data and Safety Monitoring Board (DSMB), whose remit is to protect the ethical and safety interests of the patients. The purpose of this paper is to describe a formal approach to safety monitoring, using a sequential safety procedure to aid the decisions made by the DSMB. This procedure is designed to recommend termination of the study as soon as evidence that the experimental treatment is worse than the control in terms of the primary safety response is so strong that it is unethical to proceed. The use of this formal sequential procedure enables probabilities of the study stopping erroneously and stopping correctly, under various degrees of experimental treatment disadvantage, to be examined. Also scenarios depicting data sets which lead to continuing or stopping can be presented. Such explorations are useful in encouraging all DSMB members to consider carefully, prior to the start of a study, the conditions under which they would seriously wish to consider termination. The implementation of these methods is described for three recently completed trials in which it has been used. Finally, our current recommendations for the design of these procedures, arising from these and other similar experiences, are given.