The only “mystery” surrounding erectile dysfunction drugs like Cialis and Viagra is why their creation wasn’t given priority over less-important drugs like penicillin. Otherwise, their mechanism is simple – they improve blood flow to, er, places that could benefit from improved blood flow. That’s good news for the one in 3,500 male babies who suffer from Duchenne muscular dystrophy (DMD): Researchers from Cedars-Sinai hospital in LA have found that tadalafil and sildenafil also improve blood flow to muscles starved of oxygen by the disease.

“The effects were immediate and dramatic, raising the question: If a single dose restores blood flow to muscle while the drug is in the patient’s system, could ongoing tadalafil administration provide sustained benefits, possibly preserve muscle and slow disease progression? If so, this would offer a new therapeutic strategy for DMD, and we have launched a randomized Phase III clinical trial to find out,” said Ronald Victor, MD, director of the Cedars-Sinai Center for Hypertension, associate director of clinical research at the Heart Institute and the Burns and Allen Chair in Cardiology Research.

The underlying problem with DMD is dystrophin, a protein found in the membranes of muscle cells that the disease eliminates. Victor led a research team that in 2000 discovered that the blood flow abnormality in the muscles of children with DMD was caused by a loss of nitric oxide, a signaling chemical that normally tells blood vessels to relax during exercise, increasing blood flow and oxygenation.

It’s not surprising, then, that tadalafil and sildenafil appear to have a positive effect – nitric oxide is the same chemical that tells the muscles in the penis to relax and allow blood in, creating an erection. In patients with ED, the cause is often insufficient nitric oxide, hence the Viagra and/or Cialis prescription. Victor and his team first tested the drugs on mice with dystrophin, eventually moving to human trials and publishing results in 2012 showing that tadalafil restored blood flow for boys with Becker muscular dystrophy, a similar but less extreme disease.

For boys with DMD, gripping exercises were demonstrably easier after a single dose of tadalafil or sildenafil. The drug allowed the major artery of the arm and the blood vessels in muscles of the forearm to function normally, like those of healthy boys in the same age group.

“Steroids and cardiac-protective blood pressure medication are increasingly prescribed at early ages for patients with Duchenne muscular dystrophy in an effort to delay by a few years the most devastating effects of the disease. But these treatments have no effect on the blood vessel dysfunction that prevents muscles from getting the oxygen they need,” said Victor. “In contrast, in our study, a single dose of tadalafil or sildenafil had an immediate effect. These are well-studied, well-tolerated drugs that are already on the market. If additional study confirms their benefits, repurposing the drugs for muscular dystrophy patients could quickly transform clinical practice.”