Risk

The risk for a disease or adverse event represents the probability for the event to occur among a defined susceptible (or exposed) population. For example, the risk of developing a skin rash in the first week of treatment in patients receiving an antimicrobial. When risk is presented as a proportion (per 100 patients), we assume that all patients were exposed for the same length of time. In the examples above, all subjects were observed for 1 week. However, it is expected that the longer a person is exposed, the higher is the probability for the event to be observed.3

Incidence rate (or incidence density rate or person-time incidence rate)

Incidence rates can be used to account for different lengths of times exposed when measuring risk.  It is a statistic that represents a summary measure of an event occurrence per population, taking into account the length of time that each member of the population was susceptible or exposed (person-time at risk). In technical terms, incidence rate of an event in a population is the ratio of new events in a specified time period (numerator) divided by the number of patients at risk during that period (denominator). For example, 1 case per 1,000 patient-years exposed, expresses 1 new case observed among 1,000 patients during one year of exposure.3

Post-marketing

Refers to the time after a drug or biological product has been approved by FDA.4

Carry-over PML

PML that develops a few months after stopping one disease modifying therapy (DMT) and starting a different DMT. In these cases, PML could have developed without causing symptoms while the patient was still on the previous DMT, or shortly after stopping the previous DMT.5

 

References

3.

Porta M (Ed.) (2014) A dictionary of epidemiology (6th ed.). New York, NY: Oxford University Press. http://irea.ir/files/site1/pages/dictionary.pdf. Accessed June 2018

4.

US Food and Drug Administration. Postmarketing Requirements and Commitments: Reports. https://www.fda.gov/Drugs/GuidanceComplianceRegulatoryInformation/Post-marketingPhaseIVCommitments/ucm064436.htm. Accessed January 2018

5.

Giovannoni G, et al. Pract Neurol. 2016; 16:389–393.