A spray that numbs the penis can help prevent premature ejaculation, doctors reported, and drugmaker Sciele Pharma Inc., a division of Japan's Shionogi, plans to file for U.S. approval next year.

Tests on more than 500 men suffering from premature ejaculation showed they were more satisfied and less distressed when they used the spray, the researchers told a meeting in San Diego of the Sexual Medicine Society of North America.

"Premature ejaculation can have a powerful negative impact on the emotional and sexual lives of men and their partners," said Stanley Althof of the Center for Marital and Sexual Health of South Florida.

There is no prescription treatment approved by the U.S. Food and Drug Administration for the condition, which Sciele estimates affects up to a third of U.S. men aged 18 to 59.

"Recently, the international sexual health community agreed that PE should be defined as ejaculation occurring within approximately one minute of penetration that causes the patient distress," Althof said in a statement.

The drug, called by the experimental name PSD502, is a combination of the numbing agents lidocaine and prilocaine.

Dr. Ira Sharlip of the University of California San Francisco and colleagues tested 300 men with premature ejaculation, asking them to apply the spray five minutes before intercourse.

The men on average had climaxed less than a minute into intercourse before the spray.

Using the spray for three months, 60 percent of the men lasted more than three minutes, Sharlip's team reported.

A second study looked at 256 men in the United States, Poland and Canada and found the drug "produced a clinically and statistically significant increase" from less than a minute to a mean of 2.6 minutes, the researchers reported.