Causality assessment of spontaneously reported adverse drug events: Comparison of WHO-UMC criteria and Naranjo probability scale

Abstract

ADRs usually do not present with unique clinical and laboratory findings making it difficult to demarcate them from the concurrent illness. For the estimation of the probability that a drug caused an adverse event several methods have been developed namely, the WHO-UMC criteria, the Naranjo probability scale, the Kramer scale and the Karch and Lasagna scale. But none of the available assessment methods have been shown to produce a precise and reliable quantitative estimation of relationship likelihood.

The present study was planned to compare the WHO-UMC causality assessment criteria and the Naranjo probability scale for determining causal relationship between the drug and the event. Randomly 100 Adverse Drug Event (ADE) reports were selected and assessed first by the WHO-UMC criteria and second, by using the Naranjo probability scale. Time needed for evaluation by these methods was also recorded. A disagreement in causality assessment was found in 31% cases (κ=0.214). Mean time taken while using WHO-UMC criteria was 5.3±0.37 minutes vs. 13.26±1.33 minutes while using the Naranjo probability scale. In conclusion disagreement exists amongst the WHO-UMC criteria and the Naranjo probability scale but the former method is simple and less time consuming.