TORONTO—Solifenacin and oxybutynin immediate release (OIR) achieve similar reductions in overactive bladder (OAB) symptoms, but solifenacin is associated with fewer adverse effects, according to researchers.

The finding is based on the VECTOR (VEsicare in Comparison To Oxybutynin for overReactive bladder patients) study, in which 132 OAB patients were randomized to receive either solifenacin 8 mg once a day (68 patients) or oxybutynin immediate release (OIR) 5 mg three times a day for eight weeks (64 patients). Fifty-two patients in the solifenacin group and 40 in the OIR group completed the study.

Both medications were associated with similar significant reductions in diary-recorded (OAB) symptoms and in scores on the Patient Perception of Bladder Condition measure and the Overactive Bladder Questionnaire.

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However, 35% of solifenacin subjects experienced dry mouth compared with 83% of those taking OIR. Solifenacin was associated with significantly less severe dry mouth, and fewer subjects taking this agent withdrew from the study than those on OIR.

“We were actually a little surprised to not detect a difference in effectiveness between the two treatments, but the study wasn’t powered to detect a difference,” said primary investigator Sender Herschorn, MD, Professor and Chair of Urology at the University of Toronto.

Meeting attendee Roger Dmochowski, MD, Professor of Urologic surgery at Vanderbilt Medical Center in Nashville, Tenn., commented that the study did indeed show “a clear difference” between the two agents in terms of dry mouth, “a very bothersome and problematic side effect.”