Causality assessment: the investigator's judgment and the CRC's contribution — Safety Reporting and Pharmacovigilance for CRCs

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The full CRC track covers 8 courses from study start-up to close-out — the skills sponsors actually look for.

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The anticoagulant question

A participant enrolled in a Phase III anticoagulant trial develops gastrointestinal bleeding two weeks after starting the study drug. The bleeding is clinically significant -- hemoglobin drops two grams per deciliter, and the participant requires a two-day hospitalization for observation and blood transfusion. This is, without question, a serious adverse event.

But is it related to the study drug?

The answer seems obvious at first glance. Anticoagulants thin the blood. Thinner blood bleeds more easily. Gastrointestinal bleeding in a patient on an anticoagulant is biologically plausible -- you could draw the mechanistic line from drug to event in three steps. And the timing works: two weeks is well within the pharmacologically relevant window.

But then the investigator opens the participant's chart. The participant takes 325 mg of aspirin daily for secondary cardiovascular prevention -- another agent that impairs hemostasis. The participant also has a documented history of peptic ulcer disease, with two prior episodes of GI bleeding in the five years before enrollment. Suddenly the picture is less clear. Is the study drug the cause, a contributing factor, or an incidental bystander to an event that would have happened anyway?

This is causality assessment. Not a formula. Not a checklist with a definitive answer at the bottom. It is a reasoned judgment -- made by the investigator, informed by evidence that the coordinator collects -- about whether a reasonable possibility exists that the study intervention caused or contributed to the adverse event.

In Module 1, you learned that causality is the fourth independent dimension of adverse event classification, alongside severity, seriousness, and expectedness. In the previous lesson, you learned that expectedness is the sponsor's determination, assessed against the Investigator's Brochure. Causality, by contrast, is the investigator's determination, assessed against the totality of clinical evidence. And the CRC's role -- while never to make the causality judgment -- is arguably more influential here than in any other dimension of AE assessment. The investigator can only weigh what the coordinator has gathered.