Rats with brain tumors lived 42 days while injected with the cancer drug adriamycin. goal when they also got Levitra, known generically as vardenafil, the rats survived an average of 53 days. Levitra appeared to be more effective, the researchers reported in the journal Brain Research.

levitra and viagra, known generically as sildenafil, are in a class of drugs known as PDE5 inhibitors. They were originally tested as heart drugs because they increase blood flow in small vessels.

"We chose adriamycin for this study since it is one of the most effective drugs against brain tumor cell lines in the laboratory but it has very little power in animals and humans because it is unable to cross the blood-brain tumor barrier," neurosurgeon Dr. Keith Black, who led the study, said in a statement.

"The combination of vardenafil and adriamycin resulted in longer survival and smaller tumor size," Black said.

The blood-brain stop is a molecular mechanical construction that keeps harmful agents out of the brain. Brain tumors grow little blood vessels to supply themselves with nutrients and these also have a barrier, called the blood-brain tumor obstruction.

Black said the impotence drugs appear to affect the swelling blood-brain barrier but not the larger blood-brain barrier, which may help doctors use chemotherapy drugs to kill off brain tumors exclusively of damaging healthy brain tissue, he said.

(Reporting by Maggie Fox; Editing by Will Dunham and Bill Trott)