Preliminary laboratory and animal tests indicate that a drug designed to treat urinary incontinence — specifically overactive bladder — might also be effective in the treatment of erectile dysfunction in men who fail to respond to popular ED drugs such as Viagra and Cialis.
While the oral ED drugs, known collectively as PDE5 inhibitors, have helped millions of impotent men to temporarily regain erectile function, they don’t work for an estimated 30 to 35 percent of men with serious erection problems. Research scientists involved in the recent study of the erection-friendly effects of mirabegron voice optimism that the urinary incontinence pill may effectively relieve ED symptoms in some men who fail to respond to PDE5 inhibitors.
Approved by FDA in 2012
Mirabegron was first approved by the Food and Drug Administration in 2012 and sold under the brand name Myrbetriq in the United States. The drug’s developer is Astellas Pharma Inc., an international pharmaceuticals company that is headquartered in Japan.
The recent study of mirabegron’s effects on erectile function was conducted by urology and pharmacology researchers based at Tulane University Health Sciences Center in New Orleans. Their findings were published in the September 2016 issue of “BJU International.”
Mirabegron is classified as a selective beta-3 adrenoceptor agonist, which helps to control urinary incontinence by targeting beta-3 receptors located in the urinary bladder and thus easing the physiological stress associated with overactive bladder. In setting forth the objectives for their laboratory/animal study, Tulane researchers theorized that the drug might also stimulate beta-3 adrenoceptors in the smooth muscle cells located in the spongy erectile tissue of the penis. Such relaxation would allow stronger blood flow into this tissue, thus facilitating erectile function.
Human Penile Tissue Harvested
To test their theory, researchers harvested spongy erectile tissue, also known as corpus cavernosal (CC) tissue, from men undergoing penile implant surgery. In the laboratory, scientists induced contractions in this tissue by treating it with phenylephrine. When mirabegron was introduced into the same laboratory test vessels, researchers observed a relaxation of CC tissue.
Similar results were observed when mirabegron was injected into the CC tissue of live rats, although the effects seemed less impressive than when it was tested on human CC tissue. In the conclusion to their study, researchers noted that mirabegron’s relaxation of human CC tissue occurred independently of the nitric oxide-cyclic guanosine pathway that PDE5 inhibitors utilize to facilitate erection.
Additional Studies Needed
Researchers hope their findings pave the way for additional studies, including studies in which mirabegron is used in concert with PDE5 inhibitors to see if, together, they facilitate erection in patients who don’t respond to PDE5 inhibitors alone. They noted also that the degree of smooth muscle relaxation seemed to increase based on the size of the dose of mirabegron that was used.
Widely diagnosed in both men and women, overactive bladder can seriously degrade quality of life. Although the disorder is found in both men and women in relatively equal proportions, sex-specific differences are observed. In men, overactive bladder is often associated and co-diagnosed with benign prostatic hyperplasia (BPH), a noncancerous enlargement of the prostate gland.
Effects of Enlarged Prostate
In men with BPH, enlargement of the prostate gland puts added pressure on the urethra, the tube that carries urine from the bladder and semen from the ejaculatory ducts. Because the urethra passes directly through the prostate gland, the latter’s enlargement pinches the urethra, decreasing the volume of fluids it can carry.
As a result of this pressure on the urethra, the bladder wall may thicken over time, eventually weakening and losing its ability to empty fully. The combined effects of the urethral narrowing and the failure of the bladder to empty fully often lead to urinary incontinence. Overactive bladder is just one form of urinary incontinence. Its symptoms include frequent urination, a persistent urge to urinate, urinary leakage or incontinence, and frequent nighttime urination.
Scientists have been looking for ways to help impotent men who don’t respond to the effects of Viagra and the other PDE5 inhibitors. This family of drugs is named for its ability to temporarily disable the phosphodiesterase-5 enzyme, which can interfere with blood flow to the penis, making it difficult or even impossible to achieve and maintain an erection.
Mike Wyllie, a member of the team that developed Viagra and currently the chief scientific officer of U.K.-based Plethora Solutions, told DailyMail.com that the Tulane study is an “important step” in finding help for men who don’t respond to PDE5 inhibitors.
“It has become obvious that for every patient satisfied with PDE5 inhibitors, there is one who gets an inadequate erection,” said Wyllie. “So we really do need a treatment for this group of patients.”
Johns Hopkins Study
A team of researchers at Johns Hopkins University plans to conduct clinical trials to further explore the ability of mirabegron to overcome ED symptoms in men with overactive bladder. Plans for the upcoming study were first announced in September 2016. The study is scheduled to be completed by December 2017.
The Johns Hopkins study will recruit a study group of male overactive bladder patients who also suffer from mild to moderate ED. Volunteers must be between the ages of 18 and 70. Participants in the clinical trial will be given a daily dose of mirabegron ranging from 25 to 50 milligrams. They will be tested at regular intervals to determine the drug’s effects on both their urinary incontinence and erectile dysfunction symptoms.
Collaborating with Johns Hopkins in the upcoming study will be Astellas Pharma US Inc., the American subsidiary of the company that holds the patent on Myrbetriq, the brand-name formulation of mirabegron as sold in the United States. In the United Kingdom, Astellas Pharma sells mirabegron under the brand name Betmiga.
Side Effects of Mirabegron
As with most prescription medications, mirabegron has been linked to certain side effects, some of which are similar to those associated with PDE5 inhibitors. The most common side effects of mirabegron include bloating, blurred vision, constipation, dizziness, diarrhea, dry mouth, fatigue, headache, increased blood pressure, joint pain, memory problems, nausea, and stomach pain. Most of the foregoing side effects tend to be mild and often disappear altogether upon continued use of the drug.
Mirabegron’s more serious side effects include rapid heartbeat, difficulty or pain upon urination, and sharply elevated blood pressure, the symptoms of which can include anxiety, buzzing in your ears, confusion, severe headache, shortness of breath, and uneven heartbeats. Patients experiencing these more serious side effects should seek immediate medical attention.
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