Background: α1-Adrenoceptor blockers
(α1Bs) are used for the treatment of benign prostatic hyperplasia and
hypertension, but they are known to cause hypotension-related adverse events.
The objective of the present study was to evaluate the
onset time profiles for syncope associated with the use of α1Bs. Methods: We analyzed the data obtained from the Japanese Adverse Drug Event Report (JADER) database for a period from April 2004 until November 2016 and calculated reporting
odds ratios (RORs) for eight α1Bs
available on the Japanese market, using disproportionality analysis. Moreover,
time information recorded in the JADER database was analyzed to evaluate the
onset times of adverse events. Results: In total, 186,724 reports for males
older than 20 years were analyzed. Significant RORs for syncope, with 95% confidence intervals, were obtained for naftopidil (2.53, 1.81 - 3.53), silodosin (4.24, 2.37 - 5.20), and tamsulosin (2.22, 1.75 - 2.81). The median onset times of syncope for naftopidil, silodosin, and
tamsulosin were 37, 26, and 108 days, respectively. The shape parameters
obtained by fitting the data for the three α1Bs to the Weibull distribution were all less than
1.0, indicating that all these drugs could be classified as the early failure type. The cumulative
incidence rates showed that the onset times of syncope tended to be similar
among the three α1Bs. Conclusions: Patients treated with selective α1Bs
should be closely monitored for 100 days, especially in the first 20 to 40 days
after initiation of silodosin or naftopidil. This information may be useful for
patients and healthcare professionals in preventing syncope due to the use of selective α1Bs.