One method of screening for signals for drugs in the United Kingdom that are under intensive monitoring (‘Black Triangle’ drugs) is to use both the PRR and the chi-square statistic.
One method of screening for
signals for drugs in the United Kingdom that are under intensive monitoring
(‘Black Triangle’ drugs) is to use both the PRR and the chi-square statistic. A
cut-off for each can be used; for example, a PRR > 2 and chi-squared > 4
and the number of reports > 2.
When this method is first used with these criteria on an existing database,
many of the signals generated will already be known problems. In the first
usage at the UK MCA, slightly more than 60% were known, for example uveitis with
rifabutin. About 15% were not believed to be caused by the drug but were events
or effects of disease or a function of the patient population being treated,
for example haemoptysis with dornase alpha. About 25% were new signals that
required more detailed evaluation, for example renal failure with losartan.
In general, the method is used
for continuing moni- toring so that known problems will not constitute a new
signal. The triggers that constitute a signal will then be a change in PRR to
raise it above the threshold or a 30% increase in PRR previously above thresh-
old, but where the previous judgement was that the (small) raised PRR was not
sufficient evidence of a signal.
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