risk of developing lifethreatening ventricular arrhythmia associated with tefenadine in comparison with overthecounter antihistamines ibuprofen and clemastine an observational historical cohort evaluation was performed to examine the hypothesis that terfenadine seldane exposure increases the risk of developing lifethreatening ventricular arrhythmias the study population consisted of medicaid recipients from 4 states that were included in the computerized online medical pharmaceutical analysis and surveillance system compass the drug exposure period was defined prospectively as 30 days in all treatment cohorts the primary end point was the development of lifethreatening ventricular arrhythmias ventricular tachycardia fibrillation and flutter and cardiac arrest and sudden death the comparison cohorts included terfenadine n 181672 overthecounter antihistamines n 150689 ibuprofen n 181672 and clemastine tavist n 83156 over the exposure period a total of 317 lifethreatening ventricular arrhythmic events occurred 244 of which were cardiac arrests the incidence of total lifethreatening ventricular arrhythmic events and cardiac arrests were more frequent in patients receiving overthecounter antihistamines relative risk 036 than in those receiving terfenadine a finding that was consistent across all subgroups there was no increased risk of lifethreatening ventricular arrhythmias in the terfenadine cohort as compared with the ibuprofen cohort relative risk 062 and in some analyses the ibuprofen cohort had a significantly higher arrhythmic event rate in all comparisons with the clemastine cohort the terfenadine cohort had a statistically indistinguishable relative risk 108 age race sex and cardiovascular risk were all considered in the adjusted relativerisk analyses no baseline historical characteristic or imbalance of baseline medications explained the differences between groupsabstract truncated at 250 words