Common Terms used in Pharmacovigilance

Pharmacovigilance has its own unique terminology that is important to understand. Most of the following terms are used within this article and are peculiar to drug safety, although some are used by other disciplines within the pharmaceutical sciences as well.


  • Adverse Drug Reaction is a side effect (non intended reaction to the drug) occurring with a drug where a positive (direct) causal relationship between the event and the drug is thought, or has been proven, to exist.
  • Adverse event (AE) is a side effect occurring with a drug. By definition, the causal relationship between the AE and the drug is unknown.
  • Benefits are commonly expressed as the proven therapeutic good of a product but should also include the patient’s subjective assessment of its effects.
  • Causal relationship is said to exist when a drug is thought to have caused or contributed to the occurrence of an adverse drug reaction.
  • Clinical trial (or study) refers to an organised program to determine the safety and/or efficacy of a drug (or drugs) in patients. The design of a clinical trial will depend on the drug and the phase of its development.
  • Control group is a group (or cohort) of individual patients that is used as a standard of comparison within a clinical trial. The control group may be taking a placebo (where no active drug is given) or where a different active drug is given as a comparator.
  • Dechallenge and Rechallenge refer to a drug being stopped and restarted in a patient, respectively. A positive dechallenge has occurred, for example, when an adverse event abates or resolves completely following the drug’s discontinuation. A positive rechallenge has occurred when the adverse event re-occurs after the drug is restarted. Dechallenge and rechallenge play an important role in determining whether a causal relationship between an event and a drug exists.
  • Effectiveness is the extent to which a drug works under real world circumstances, i.e., clinical practice.
  • Efficacy is the extent to which a drug works under ideal circumstances, i.e., in clinical trials.
  • Event refers an adverse event (AE).
  • Harm is the nature and extent of the actual damage that could be or has been caused.
  • Implied causality refers to spontaneously-reported AE cases where the causality is always presumed to be positive unless the reporter states otherwise.
  • Individual Case Study Report (ICSR) is an adverse event report for an individual patient.
  • Life-threatening refers to an adverse event that places a patient at the immediate risk of death.
  • Phase refers to the four phases of development: I – small safety trials early on in a drug’s development; II – medium-sized trials for both safety and efficacy; III – large trials, which includes key (or so-called “pivotal”) trials; IV – large, post-marketing trials, typically for safety reasons. There are also intermediate phases designated by an “a” or “b”, e.g. Phase IIb.
  • Risk is the probability of harm being caused, usually expressed as a percent or ratio of the treated population.
  • Risk factor is an attribute of a patient that may predispose, or increase the risk, of that patient developing an event that may or may not be drug-related. For instance, obesity is considered a risk factor for a number of different diseases and, potentially, ADRs. Others would be high blood pressure, diabetes, possessing a specific mutated gene, for example, mutations in the BRCA1 and BRCA2 genes increase propensity to develop breast cancer.
  • Signal is a new safety finding within safety data that requires further investigation. There are three categories of signals: confirmed signals where the data indicate that there is a causal relationship between the drug and the AE; refuted (or false) signals where after investigation the data indicate that no causal relationship exists; and unconfirmed signals which require further investigation (more data) such as the conducting of a post-marketing trial to study the issue.
  • Temporal relationship is said to exist when an adverse event occurs when a patient is taking a given drug. Although a temporal relationship is absolutely necessary in order to establish a causal relationship between the drug and the AE, a temporal relationship does not necessarily in and of itself prove that the event was caused by the drug.
  • Triage refers to the process of placing a potential adverse event report into one of three categories: 1) non-serious case; 2) serious case; or 3) no case (minimum criteria for an AE case are not fulfilled).

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