Combination of alfuzosin and tadalafil exerts an additive relaxant effect on human detrusor and prostatic tissues in vitro

Background: Lower urinary tract symptoms (LUTS) suggestive of benign prostatic hyperplasia (BPH) and erectile dysfunction (ED) are highly prevalent in aging men and are strongly linked. Alpha₁-blockers such as alfuzosin are effective monotherapies for LUTS. Phosphodiesterase type 5 (PDE5) inhibitors such as tadalafil are the first-line treatment for ED. Both drugs act by two different mechanisms of action on common urogenital target organs and, thus, may have additive effects.

Objectives: We evaluated in vitro the effects of alfuzosin, tadalafil, and the combination of both on human detrusor and prostatic smooth muscle.

Design, setting, and participants: Prostatic and bladder tissue were obtained from patients (n=20 and n=17, respectively) undergoing cystoprostatectomy for bladder cancer.

Measurements: In organ baths, isolated prostatic strips and isolated bladder strips were incubated with vehicle, tadalafil (10⁻⁶ M and 10⁻⁵ M), alfuzosin (3×10⁻⁸ M or 10⁻⁶ M and 10⁻⁵ M) or a combination. Concentration-response curves (CRCs) to norepinephrine were generated on prostatic strips and detrusor strips precontracted with carbachol. Strips were also submitted to electrical field stimulation (EFS).

Results and limitations: When alfuzosin and tadalafil were combined, the maximal relaxation to norepinephrine on carbachol-precontracted detrusor strips was significantly increased compared with tadalafil alone, and EFS-induced detrusor contractions were better inhibited compared with each compound alone. Tadalafil significantly inhibited norepinephrine-induced prostatic strip contractions by reducing the maximal effect, whereas alfuzosin shifted the CRC of norepinephrine to the right. Combining both tadalafil and alfuzosin resulted in a greater relaxant effect. Likewise, the combination was more effective at reducing EFS-induced contractions compared with each compound alone.

Conclusions: The combination of alfuzosin and tadalafil exerts an additive effect of inhibiting adrenergic smooth muscle tone of prostatic tissue and EFS-induced detrusor contractions and conversely, of enhancing adrenergic relaxation of detrusor precontracted with carbachol. These experiments provide experimental support for the clinical investigation of the combination of α1-blockers and PDE5 inhibitors in the treatment of LUTS.