COMPARING THE TOXICITY OF 2 DRUGS IN THE FRAMEWORK OF SPONTANEOUS REPORTING - A CONFIDENCE-INTERVAL APPROACH

Spontaneous reporting remains the most frequently used technique in po st-marketing surveillance. Decision making usually depends on comparis ons between the number of adverse drug reactions (ADRs) reported for t wo drugs on the basis of an equivalent number of prescriptions. The va lidity of such comparisons is expected to be jeopardized by probable u nderreporting of ADR cases. This problem is accentuated when it cannot be assumed that the magnitude of underreporting is the same for the b oth drugs. Differences in reporting ratios can overemphasize, cancel, or reverse the conclusions of a statistical comparison based on the nu mber of reports. We propose a single method for (1) calculating confid ence intervals for relative risks estimated in the context of spontane ous reporting and (2) deriving the range of reporting ratios for which the conclusion of the statistical comparison remains statistically va lid.