TAS-303 effects on urethral sphincter function in women with stress urinary incontinence: phase I study

TAS-303, which selectively inhibits noradrenaline reuptake, was developed for treating stress urinary incontinence (SUI). The proximal urethra mainly comprises smooth muscle fibers in which α1 adrenergic receptors are abundant. This study was conducted to evaluate the effect of TAS-303 on urethral function and its safety profile in female patients with SUI.

In total, 16 women (age, 20-64 years) with SUI and > 5.0 g of leakage in the 1-h pad test at screening were randomized and administered the assigned treatment in a double-blind manner. The primary end point was change in the maximal urethral closure pressure (MUCP) at 6 h post-dose. The secondary end point was change in the urethral closure pressure of the entire urethra and each urethral region (proximal, middle, and distal) at 6 h post-dose. The results were analyzed using a t-test.

The mean change ± standard deviation in MUCP at 6 h post-dose was 3.473 ± 12.154 cmH₂O for TAS-303 and 2.615 ± 9.794 cmH₂O for placebo (between-group difference: 0.858 cmH₂O, P = 0.8047). The mean changes ± standard deviation in urethral closure pressure of the proximal urethra at 6 h after the administration of TAS-303 18 mg and placebo were 3.863 ± 10.941 and 1.634 ± 12.093, respectively (between-group difference: 2.229 cmH₂O, P = 0.5976).

No significant difference in MUCP and urethral closure pressure was found between TAS-303 and placebo. However, the change in the proximal urethral closure pressure with TAS-303 was larger than that with placebo. This suggests that TAS-303 has pharmacological effects on urethral sphincteric function.