Vesnarinone-induced WBC disorders in Japan.

Vesnarinone is a new oral inotropic agent that augments myocardial contractility with little effect on heart rate or myocardial oxygen consumption. In Japan, vesnarinone was approved in June 1990 and first marketed in September 1990. Although the efficacy of vesnarinone has been confirmed, WBC disorders, which are principal adverse events associated with the use of vesnarinone, were found after marketing was begun in Japan. This survey was carried out to estimate the incidence of WBC disorders, the predominant periods in which these adverse events develop, and the effects of risk factors in the cohort of patients who have been administered vesnarinone since its market release in Japan. Data were available for 14,921 patients who took vesnarinone at least once during the period from 1 March 1991, through 28 February 1994. Vesnarinone-induced agranulocytosis, which is usually evidenced by a sharp decrease in granulocyte count, was seen in 0.25% of the patients. The cumulative incidence of agranulocytosis was 0.34% at 12 weeks. The predominant period of development was estimated to be the first 4 months after initiation of therapy, with the rate peaking in the second month. The risk of WBC disorders was higher among females.