Dechallenge and Rechallenge

Part of Pharmacovigilance and Drug Safety (PV) Training: Causality.

About 2 minutes. Free, in your language, no account needed.

The strongest evidence available in a single case

A positive dechallenge, where the event improved or resolved after the product was stopped or the dose reduced, is among the most informative facts a case can carry.

A positive rechallenge, where the event returned on re-exposure, is stronger still. In a single patient it is close to the best evidence that exists.

Why they are often missing

Because nobody asked. The reporter knows, and the question was not put to them.

It is also frequently missing because the patient was never taken off the product, which is itself a fact worth recording. "Drug continued, event resolved" points in a different direction from "drug stopped, event resolved."

What a negative result means

A negative dechallenge, where the event persisted after stopping, does not exclude causality. Some drug-induced injuries do not reverse. Hepatic injury, some skin reactions and anything structural may persist long after the exposure ends.

So a negative dechallenge is evidence, weighed with everything else, not a disproof.

Rechallenge is not something you request

Deliberate re-exposure to find out whether a drug caused a serious event is an ethical question for a clinician with the patient in front of them, not a data-gathering exercise. Where a rechallenge has happened, record it fully. Where it has not, do not suggest it.

Recording the categories honestly

Most systems offer positive, negative, not done and unknown for each. "Not done" and "unknown" are different: the first says the product was never stopped, the second says nobody knows what happened when it was. Using them interchangeably destroys the value of the field.