Authors: Gerald L. Klein, MD*; Roger E. Morgan*, MD; Angela Overton, MSc**; Mark Tulchinskiy, MD*; Johannes Wolff*, MD/PhD*; Freddy Byrth*; Marion Stamp-Cole*
MedSurgPI* Prevail InfoWorks, Inc.**
Why is it so important to determine the relationship of a Serious Adverse Event (SAE) or Adverse Event (AE) to the investigational product (IP)?
Consequences of incorrectly attributing causality to the Investigational Product (IP) despite a lack of reasonable evidence linking the drug to the adverse event:
May prevent product approval due to significant SAEs or the quantity of AEs and SAEs.
May impact the product label, reduce medication adoption by prescribers.
May impose unnecessary burden on patients and health care providers (HCPs) by means of FDA mandating REMS (Risk Evaluation and Mitigation Strategy.
Consequences of assigning unrelated causality to the IP when there is evidence of relatedness:
Unsafe drug may be approved.
A drug could receive approval with faulty/misleading information regarding the balance of safety and efficacy.
Safety drug-use mitigation strategies may not be considered and implemented.
It can cause unnecessary patient harm.
The development of supportive care guidelines may be inaccurate.
What does it mean that an SAE or AE is possibly related?
Just because there is a temporal relationship between AE/SAE and the drug, there could still be a critical judgment for reasonable possibility. The Principal Investigator (PI) should not blindly follow the ancient Greek maxima “Post hoc ergo proper hoc”, that means “after this therefore because of this”. Instead, the PI should consider these factors when evaluating AE causality:
Associations and Sources
Consider whether the event is associated with the IP or a concomitant medication, intercurrent disorder, disease progression, or comorbidity.
Rely on the Investigator’s Brochure (IB), preclinical research, medical literature on the studied product, and similar drugs for essential information.
Modifying Factors
Overdose and incorrect administration (for example, the wrong frequency or route) can impact AEs.
Assess drug interactions that may increase toxicity.
Be aware of subjects inadvertently taking excluded drugs, herbs, or supplements during the trial.
Significant changes in diet or nutritional status may also be a factor.
Modification of psychological status may become a stimulating factor.
Patient History
Differentiate between exacerbations of past medical history and comorbidities and new AEs.
Consider symptoms occurring before exposure to the IP.
For an explanation of the standard WHO causality classification system, please follow this link.
Causality Factors to Consider
Has there been a dechallenge/rechallenge of the product?
Biological gradient criterion states that a dose-response effect is a strong argument for causation. If a subject received 5mg of a drug and had a mild headache, and the headache increased when the dose increased, there is a dose-response effect. Similarly, aggregate data, occurrence percentages, and dosage can be correlated.
Plausibility: the causal relationship between the AE and the IP must be biologically possible and logical. For example, if a subject receives a new type of aspirin formulation and their blood pressure (BP) increased, it is not plausible that the BP change is related to the aspirin.
Coherence refers to assessing whether the facts align with the natural history and biology of the disease. The data may support an extension or exacerbation of the disease, which is frequently seen in oncology studies.
Example: In metastatic breast cancer, a patient develops anemia, which is known to occur in this disorder.
Have experimental epidemiologic or other objective (preclinical or clinical) studies demonstrated similar causality?
Does an analogy exist, meaning a similar drug has caused the same type of AE under comparable circumstances? This is frequently seen as a class effect in similar drugs. For example, beta blockers may cause bradycardia.
When is a laboratory test result an AE?
Many protocols state that a laboratory result is an AE if it is clinically significant in the investigator’s opinion. This frequently causes confusion.
A good rule of thumb: if the test results prompt further diagnostic studies (excluding repeats for confirmation) or leads to therapeutic action. If either occurs the laboratory results may be considered clinically significant.
Overlooked reasons which qualify as an SAE
A persistent or significant incapacity.
Substantial disruption of the ability to conduct normal life functions. [1]
References
Council for International Organizations of Medical Sciences (CIOMS). Guidelines for preparing core clinical-safety information on drugs: report of CIOMS Working Groups III and V. Geneva, Switzerland: CIOMS; 1999.
International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH). ICH E2A: Clinical Safety Data Management: Definitions and Standards for Expedited Reporting. 1994.
Naranjo CA, Busto U, Sellers EM, et al. A method for estimating the probability of adverse drug reactions. Clin Pharmacol Ther.1981;30(2):239-245.
Rothman KJ, Greenland S, Lash TL. Modern Epidemiology. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2008.
Shimonovich, M., Pearce, A., Thomson, H. et al. Assessing causality in epidemiology: revisiting Bradford Hill to incorporate developments in causal thinking. Eur J Epidemiol 36, 873-887 (2021). https://doi.org/10.1007/s10654-020-00703-7.
The Use of the WHO-UMC system or standardized case for standardised case causality assessment. https://www.who.int/docs/default-source/medicines/pharmacovigilance/whocausality-assessment.pdf.
U.S. Food and Drug Administration (FDA). Guidance for Industry: Clinical Laboratory Studies for Regulatory Submissions. Silver Spring, MD: FDA; 2018
[1] https://www.fda.gov/drugs/investigational-new-drug-ind-application/ind-application-reporting-safety-reports