Karen Weintraub

Special for USA TODAY

Cialis, normally used to treat erectile dysfunction in men, may offer promise for boys with a fatal muscle disorder.

In a preliminary study published today in the journal Neurology, the drug appears to improve blood flow to the boys' muscles, just as it boosts blood flow to the penis of men with erectile dysfunction.

The drug was given to 10 boys over a short period, so the results are far from conclusive. They do indicate that Cialis deserves more research as a treatment for the boys' disease, known as Duchenne muscular dystrophy.

"We had really striking results," said Ronald Victor, a cardiologist at Cedars-Sinai Medical Center in Los Angeles, who led the work. Examining the boys' muscle cells after treatment, he said, "it looked like a complete correction of the blood flow abnormality."

In Duchenne muscular dystrophy, boys who are apparently normal until age 4-8, suddenly start to go weak. In their 20s or sometimes earlier, their heart or diaphragm – both muscles – give out, and they die.

The genetic glitch that causes the disease robs the body of its ability to produce a muscle protein called dystrophin, which provides structure to muscles and helps send cellular signals. Without dystrophin, muscle cells are unable to repair the damage caused by exercise.

The disease is nearly exclusive to boys, because the gene that makes the protein occurs twice in girls but only once in boys, so damage to one copy will cause the disease.

Curing the Duchenne probably will take a multi-pronged approach. Treatment with Cialis could prove effective enough to become part of that approach, said Pat Furlong, founding president and CEO of Parent Project Muscular Dystrophy, an advocacy group.

Cialis almost certainly won't change the course of the disease, but, she said, "if it provides more nutrition to muscles through the blood supply, if it provides more energy to the children, and more endurance on those skeletal muscles, then that contributes to the whole of what we're trying to accomplish for these kids."

Drugs are under development to support muscle and boost the production of dystrophin. Blood pressure drugs and the cancer drug tamoxifen are being explored to see if they offer benefits to Duchenne patients, Furlong said.

Cialis did lead to some side effects, the new study showed. Several of the boys had prolonged erections while taking the drug – one for six hours – though Victor said they were not reported to be painful.

A lower dose of the drug, comparable to what men take for erectile dysfunction, appeared to normalize blood flow to the boys' skeletal muscles. A higher dose, used for some breathing problems, enabled the boys' muscles to recover after exercise, Victor said.

Researchers also tested the erectile dysfunction drug Viagra but found it had to be taken more often than Cialis – as much as three times a day – and couldn't be taken with food.

Victor has begun testing Cialis in a larger, longer-term study funded by the drug's manufacturer, Eli Lilly, to see whether it will provide noticeable benefits to those with Duchenne.