Shah evaluated the impact of various medications on the corrected QTc interval. Approval of a new medication must take into account its risk for causing torsades de pointes in a patient.
Factors indicating a high potential risk for torsades de pointes - one or both of the following:
(1) an increase of the corrected QTc at peak effect from baseline >= 60 milliseconds
(2) a post-dose corrected QTc interval >= 500 milliseconds (irrespective of baseline QTc)
The potential risk for torsades de pointes can be estimated for a drug based on the maximum increase in the QTc interval over baseline. This may or may not coincide with the peak concentration of the drug, since metabolites may also affect the risk.
increase in QTc in milliseconds =
= (maximum corrected QTc during therapy in ms) - (baseline corrected QTc)
Increase in QTc
Potential for Drug to Cause Torsades
0 to 5 milliseconds
very unlikely
6 to 10 milliseconds
probably not
11 to 15 milliseconds
possibly
16 to 25 milliseconds
probably
>= 26 milliseconds
very likely
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