Researchers at Cedars-Sinai Medical Center reported Wednesday that in a small group of boys with Duchenne muscular dystrophy (DMD), the erectile dysfunction treatment drugs sildenafil (Viagra) and tadalafil (Cialis) helped to normalize the blood flow in exercising muscle, which is markedly impaired in DMD. The study also revealed that the ability of DMD patients’ muscles to receive increased blood flow during exercise by way of reduced sympathetic tone is impaired and not improved by current standard of care treatments with corticosteroids alone or in combination with heart-protecting medication.

Duchenne muscular dystrophy is a genetic disorder that affects boys and young men. The disease results from the patient’s inability to produce sufficient amounts of a protein called dystrophin, which is integral in the synthesis of nitric oxide. Nitric oxide is crucial for signaling blood vessels to open up and allow more blood to flow through them during exercise so that the working muscle’s energy and oxygen demands are met and wastes and carbon dioxide are adequately removed.

“Boys with Duchenne muscular dystrophy have a blood flow abnormality — delivery of blood and oxygen to their muscles — that does not increase the way it should during mild exercise,” said lead researcher Dr. Ronald Victor, the associate director of the Cedars-Sinai Heart Institute in Los Angeles.

For DMD patients, the future has for a long time been grim. Boys with DMD historically did not live beyond their teens. More recently, their lives are extending into their 30s and in some cases even into their 40s and 50s. Advances in care are credited. Steroidal treatments can slow muscle degeneration and protect the heart and lungs. However, there is no cure, and resolving the blood flow problem has remained elusive.

What is significant about this new study, which was conducted with 10 boys aged 8 to 13 years with DMD and 10 healthy control boys, is that the authors identified as a new protein target for DMD therapy the target of both Viagra and Cialis—phosphodiesterase type 5 (PDE5). Inhibition of PDE5 by either Viagra or Cialis results in decreased sympathetic tone, which allows blood vessels to dilate, or open up. Dilation of blood vessels once sympathetic tone is reduced increases blood flow through the vessels.

“A few boys in our study had erections after taking these drugs,” Victor noted. “The erections were not painful and not dangerous and resolved spontaneously without treatment.”

According to Victor, the study paved the way for a much larger study to confirm the results and to determine whether targeting PDE5 can prevent or at least slow the degeneration associated with DMD.

The report was published in the May 7 issue of Neurology.