Is mirabegron effective as an add-on to tamsulosin treatment for overactive bladder in men with lower urinary tract symptoms?

This paper investigated the effectiveness and safety of mirabegron (Myrbetriq) as an add-on treatment to tamsulosin (Flomax) for the treatment of overactive bladder (OAB) in men with lower urinary tract symptoms (LUTS). This study found that mirabegron appeared to be effective for the treatment of OAB symptoms in those treated with tamsulosin for LUTS.

LUTS is a collection of symptoms which may include OAB, urine leakage (incontinence), or discomfort passing urine. OAB is characterized by having a strong urge to urinate and being woken up at night due to the need to urinate (nocturia). Tamsulosin is a commonly used treatment for LUTS. It works by relaxing the muscles in the prostate and the bladder. Tamsulosin may not be effective enough to improve the symptoms of OAB. 

The first treatment for OAB is antimuscarinic drugs such as tolterodine (Detrol) or solifenacin (Vesicare). However, these drugs are associated with side effects such as dry mouth, retention of urine, and constipation. Mirabegron is another drug used to treat OAB symptoms. It acts to relax the muscles around the bladder to improve urine storage. The effectiveness of mirabegron for OAB in men receiving tamsulosin for LUTS is not clear.

This study included 568 men with OAB who were treated with tamsulosin for LUTS. Participants were randomly split into 2 groups of equal sizes. All patients received tamsulosin 0.2 mg plus placebo for 4 weeks. Patients in group 1 then received a placebo plus tamsulosin 0.2 mg and patients in group 2 received mirabegron 50 mg and tamsulosin 0.2 mg for 12 weeks. The average number of urinations in 24 hours was the primary outcome measured. 

The average number of urinations in 24 hours was reduced by 1.27 in group 2 compared to a 0.75 reduction in group 1. The average volume of urine released per urination was also improved in those treated with mirabegron.

Patient-reported outcomes also showed an improvement in OAB following treatment with mirabegron. 3.9% of those who received mirabegron and 6.3% of those who received the placebo reported drug-related side effects. However, most of these were mild or moderate.

This study suggested that mirabegron is an effective add-on to tamsulosin for the treatment of OAB in men with LUTS.

This study included Japanese and Korean men only. Therefore the results may not be applicable for men elsewhere. This study was funded by Astellas, the manufacturer of mirabegron.