Viagra 'could help treat Duchenne muscular dystrophy'
Viagra and Cialis, normally used for treating male impotence, could be used to fight a muscle-wasting disorder which affects boys, say US scientists.
In tests the drugs helped improve blood flow to the muscles of boys with Duchenne muscular dystrophy (DMD).
They hope it could slow the onset of the disease, which causes the breakdown and gradual loss of muscle fibres.
Experts said the study could be beneficial but would not necessarily improve the boys' ability to walk.
DMD affects one in every 3,500 newborn boys, and many will die before they reach 30.
It can become fatal when it affects the muscles needed to breathe and pump blood around the body.
Many patients with the condition have to use a wheelchair by the age of 10, and there is currently no effective treatment.
Blood flow changes
Corticosteroids, currently used for short-term treatment, have a range of side effects, from acne, muscle weakness and stomach ulcers to diabetes, osteoporosis and high blood pressure.
But they do not work in 25% of cases.
In this study, scientists at the Cedars-Sinai Institute in Los Angeles tested the effect of at the new treatment in a study of 10 boys with DMD aged between eight and 13 who had blood flow problems.
They were given a single dose of either sildenafil, commonly known as Viagra, or tadalafil, known as Cialis, which is also used to treat erectile dysfunction.
Scientists then measured blood flow in the boys' muscles when they were resting and doing a handgrip exercise before comparing it to measurements in 10 boys of the same age who didn't have DMD.
'Immediate and dramatic'
After treatment with both of the drugs, blood flow in the boys' muscles was restored to a healthy level, the study said.
Lead researcher Dr Ronald Victor, at the Cedars-Sinai Institute, told the BBC the research was a "bridge" from the study in mice into a larger, 48-week human study to try out the treatment in 300 boys across the world.
Dr Victor said the effect was "immediate and dramatic".
He added: "If you can restore the blood flow you might be able to slow the disease progression, but not cure it."
He said there "may be some embarrassment" with the usual effect of Viagra and Cialis but that he hoped a correct dose would be found in the larger trial.
Ability to walk
Prof Steve Winder, at the University of Sheffield, said the study was a "proof of principle" which "might have a small beneficial effect".
But Prof Winder added: "What it does not address is if treating boys with DMD with Viagra actually improves their ability to walk.
"There is no evidence this stops the muscle atrophy."
He said a boy's ability to walk was the "best measure of treatment".
Prof Winder said the treatment might be used with another to come through but that it was not a "big breakthrough" in treating DMD.
Dr Marita Pohlschmidt, director of research at the Muscular Dystrophy Campaign, said the study was "encouraging".
She said: "We now need to establish whether the improved blood flow slows the muscle-wasting and the progression of the condition and whether the long-term use is safe.
"There are potential treatments addressing the underlying genetic causes of Duchenne muscular dystrophy in clinical trials and therapies that could slow progression are vital to the many who continue to await them."