Do tamsulosin and oxybutynin have opposing effects in male patients with Benign Prostatic Hyperplasia (BPH) and overactive bladder?

From the Guidelines

Tamsulosin and oxybutynin can be used together in male patients with Benign Prostatic Hyperplasia (BPH) and overactive bladder, but their effects should be carefully balanced to avoid worsening urinary retention, as suggested by the AUA/SUFU guideline 1. When treating male patients with both BPH and overactive bladder, it's essential to consider the potential interactions between these two conditions and the medications used to treat them. Tamsulosin, an alpha-1 adrenergic receptor blocker, is commonly used to improve urine flow and reduce BPH symptoms, while oxybutynin, an anticholinergic medication, is used to treat overactive bladder symptoms.

• The typical dose of tamsulosin is 0.4 mg once daily, and it works by relaxing smooth muscle in the prostate and bladder neck.
• Oxybutynin is commonly prescribed at 5 mg twice daily or 10 mg once daily in extended-release form and works by blocking muscarinic receptors to reduce bladder muscle contractions. According to the AUA/SUFU guideline, clinicians may consider combination therapy with an alpha blocker and an antimuscarinic medication or beta-3 agonist for patients with BPH and overactive bladder 1.
• However, when using these medications together, it's crucial to monitor for increased post-void residual urine volume, as oxybutynin can potentially reduce bladder contractility and worsen urinary retention in BPH patients. Alternative approaches include using mirabegron (a beta-3 agonist) instead of oxybutynin, as it has less risk of urinary retention, or considering combination therapy with a 5-alpha reductase inhibitor like finasteride along with tamsulosin for long-term BPH management.
• The AUA/SUFU guideline suggests that antimuscarinics and beta-3 agonists are effective in treating overactive bladder in men with BPH, and while antimuscarinic medications may increase post-void residual volumes slightly, they do not appear to be associated with a significant increased risk of urinary retention among groups of patients with co-existing bladder outlet obstruction secondary to BPH 1.

From the Research

Tamsulosin and Oxybutynin Effects in Male Patients

• Tamsulosin is a subtype-selective alpha(1A)- and alpha(1D)-adrenoceptor antagonist used to treat lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH) 2, 3.
• Oxybutynin is an antimuscarinic agent used to treat overactive bladder symptoms 4.
• The combination of tamsulosin and oxybutynin has been studied for the treatment of LUTS and overactive bladder in men 5, 4.

Efficacy of Combination Therapy

• A randomized controlled trial found that the combination of tolterodine (an antimuscarinic agent similar to oxybutynin) and tamsulosin provided significant improvements in LUTS and overactive bladder symptoms compared to placebo or monotherapy 5.
• Another study found that the combination of extended-release oxybutynin and tamsulosin resulted in significantly greater improvement in total International Prostate Symptom Score (IPSS) compared to tamsulosin alone 4.

Safety and Tolerability

• The combination of tamsulosin and oxybutynin was found to be well tolerated, with a low incidence of adverse events such as acute urinary retention and postvoid residual volume higher than 300 mL 4.
• The incidence of peak flow rates below 5 mL/s was similar between combination therapy and tamsulosin alone 4.

Opposing Effects

• There is no evidence to suggest that tamsulosin and oxybutynin have opposing effects in male patients with BPH and overactive bladder 2, 3, 5, 4, 6.
• In fact, the combination of these two agents has been shown to be effective and well tolerated in the treatment of LUTS and overactive bladder in men 5, 4.