Kava hepatotoxicity: comparative study of two structured quantitative methods for causality assessment

Background and objective: Ingestion of the medicinal herb kava has been associated with hepatotoxicity. We aimed to compare two different quantitative methods of causality assessment of patients with assumed hepatotoxicity by the herb. Methods: We assessed causality in 26 patients from Germany and Switzerland, using two structured quantitative analytical methods: the system of Maria and Victorino (MV) and that of the Council for International Organizations of Medical Sciences (CIOMS). In all 26 patients, regulatory ad hoc evaluation had suggested a causal relationship between liver disease and kava use. Results and discussion: Assessment with the MV scale resulted in no or low graded causality for kava in the 26 patients with liver disease. Causality was probable (n = 1), possible (n = 2), unlikely (n = 7), and excluded (n = 16). Causality for kava was more evident with the CIOMS scale: highly probable (n = 1), probable (n = 2), possible (n = 6), unlikely (n = 2) and excluded (n = 15). However, the results of both quantitative causality assessments are not supportive for most of the regulatory ad hoc causality assessments of the 26 patients. Conclusion: Grades of causality for suspected hepatotoxicity by kava were much lower when evaluated by structured quantitative causality assessment scales than by regulatory ad hoc judgements. The quantitative CIOMS scale is the preferable tool for causality assessment of spontaneous reports of hepatotoxcity involving kava.