An adverse event is any untoward medical occurrence in a subject administered a medicinal product or participating in a clinical trial. It is crucial that an adverse event can occur temporally associated with the treatment or trial, without a causal relationship already being assumed. It is thus the broadly defined starting point for systematic safety documentation.
Concept and recording in the clinical trial
According to the ICH guidelines, an adverse event, AE for short, encompasses, for example, an unfavorable sign, a symptom, a disease or an abnormal laboratory finding. The designation initially describes an observation, not its cause. A headache after administration of the investigational medicinal product, a newly diagnosed disease or a clinically significant laboratory value change can therefore be recorded as an AE, even if the underlying disease, a concomitant treatment or other circumstances are considered as an explanation.
In a clinical trial, the protocol governs which events and laboratory abnormalities are to be documented for the safety evaluation and how they are forwarded to the sponsor. Regulation (EU) No 536/2014 generally requires the recording of all adverse events, unless the protocol provides otherwise. Their complete, traceable recording creates the data basis for the medical assessment by investigator and sponsor as well as for the continuous evaluation of the investigational medicinal product.
Severity, seriousness and causality
An AE is described medically and assessed, among other things, by onset, course, outcome, intensity, concomitant medication and potential relationship to the investigational medicinal product. The intensity of a symptom and the regulatory category “serious” are not synonymous. An event is serious if it, for instance, results in death, is life-threatening, requires inpatient hospitalization or prolongation of existing hospitalization, results in persistent or significant disability or causes a congenital anomaly. Medically important events can also be considered serious.
The causality assessment answers a different question: Is there at least a reasonable possibility that the medicinal product caused the event? It is performed based on the available information and can change with new findings. The quality of the initial documentation is therefore essential. It allows the temporal relationship, alternative causes, dechallenge or rechallenge information and medical plausibility to be reliably reviewed later.
Even a relationship that is subsequently refuted does not change the fact that the initial observation was properly documented as an AE.
Distinction from adverse reaction, SAE and SUSAR
An adverse event does not contain a causality assumption. An adverse drug reaction, on the other hand, is a noxious and unintended response for which a relationship with the medicinal product is at least reasonably assumed. Therefore, not every AE is an adverse reaction, but an AE can indeed be classified as such after assessment. This conceptual separation prevents mere temporal observations from being prematurely interpreted as a medicinal product risk.
The serious adverse event, SAE, is an AE with a defined criterion of seriousness; an SAE also does not have to be caused by the medicinal product. A SUSAR is more narrowly defined: it is a suspected unexpected serious adverse reaction. For this, suspicion of causality, seriousness and unexpectedness compared to the reference safety information must come together. SUSARs are therefore not a separate stage of every AE, but a particularly regulatory-relevant subset of assessed events.
Relevance for clinical trials
Consistent AE recording is a core process of protecting trial participants. It influences safety evaluations, the assessment of individual cases and aggregated patterns, the updating of investigator information and informed consent documents and, if applicable, measures at the investigational site. Authorities and auditors check in particular whether events were completely documented, medically plausibly assessed and forwarded in accordance with the protocol and reporting procedures. Missing baseline information often cannot be robustly supplemented later.
Full-service CROs such as Mediconomics support with the establishment of clear recording pathways, with training of the investigational sites, with the review of safety data and with the alignment between monitoring, data management, pharmacovigilance and medical writing. This includes, for example, specifications for documentation in the case report form, the follow-up of missing information, medical coding and the preparation of traceable case narratives. In this way, individual events and their assessment remain consistent within the safety data flow.
Frequently Asked Questions (FAQ)
Is every adverse event an adverse reaction?
No. An AE is recorded independently of a suspected relationship. Only when a relationship with the medicinal product is at least reasonably assumed is it an adverse drug reaction.
Is a severe symptom automatically a serious adverse event?
No. “Severe” can describe the intensity. “Serious” depends on the defined consequences or medical criteria, such as hospitalization or being life-threatening.
Why are unrelated events also documented?
Complete recording enables robust later causality and pattern assessment. Without these data, potential risks of an investigational medicinal product could be overlooked or incorrectly classified.
Regulatory references
- ICH E2A “Clinical Safety Data Management” – defines AE, adverse reaction, seriousness and unexpectedness for safety reporting.
- ICH E6(R3) “Good Clinical Practice” – describes the documentation and prompt forwarding of serious events to the sponsor.
- Regulation (EU) No 536/2014, Articles 41 to 43 – governs safety reporting in clinical trials.
- EMA GVP Module VI – covers the management and reporting of suspected adverse drug reactions post-authorization.