Astellas can relax as overactive bladder drug is approved

US approval of Astellas Pharma's novel urinary incontinence drug mirabegron, now called Myrbetriq, has ticked two important boxes for the Japanese company. The green light from the FDA will help Astellas achieve its long-term goal of growing sales in the important US market as well as marking its territory in the urinary incontinence space.

The drug made it past the US regulator last week, despite previous concerns over increased blood pressure and heart rate in patients taking the once-daily oral pill (Event - Astellas looks to hold onto UI franchise after adcom vote, April 10, 2012). This means that Astellas is forecast to have the top two urinary incontinence drugs in 2018, with sales of Myrbetriq and Vesicare forecast to reach $2.22bn that year, and a big slice of the market - sales across all branded urinary incontinence drugs are forecast to reach $4bn by 2018, according to EvaluatePharma.

Driving growth

Approval of Myrbetriq is also an important win for Astellas because of the company's relatively sparse pipeline. The drug, which was approved in Japan in September 2011 under the brand name Betanis, is forecast to become the second-biggest growth driver at Astellas behind the filed prostate cancer drug enzalutamide (MDV3100).

Additionally, the launch of Myrbetriq this year will give Astellas plenty of time to mange the lifecycle of its other marketed urinary incontinence drug, Vesicare. Astellas is now almost certain to start trying to migrate patients to the new drug over the next couple of years ahead of the Vesicare patent expiry in 2018, and to reduce costs by winding down its marketing efforts for its flagship UI drug.

New mode of action

Ever heightening reimbursement and pricing pressures mean new drug launches are proving tougher than ever, but what should help Myrbetriq get off to a good start in life is its unique method of action. The product works by stimulating B3 receptors in the smooth muscles in the bladder, which results in the muscles relaxing, allowing the bladder to fill properly and reducing the urge to urinate.

At present all of the marketed products for UI are muscarinic antagonists which, while stopping involuntary bladder contractions, can prevent the bladder from emptying itself, increasing the risk of urinary retention. This is a problem particularly in men as it increases the risk of catheterisation, so Myrbetriq will offer a welcome new treatment option.

The only possible cloud on the horizon for Astellas’s domination of the UI market is the entry of the multipurpose Botox, but it is thought that this drug will initially be used in the smaller population of patients with neurological incontinence. Astellas’s drugs will also face generic competition from Pfizer’s Detrol, a traditional muscarinc agonist that goes off patent in September and could put pressure on Vesicare sales - another reason why the approval of Myrbetriq has come at an opportune time.