Drugmaker Merck says U.S. regulators have approved its vaccine Gardasil to prevent genital warts in boys, a new use for a product already given to women to prevent cervical cancer.

The Whitehouse Station, N.J.-based company says the Food and Drug Administration approved its application for use of Gardasil in boys ages 9 through 26.

Gardasil already is approved in women to block four strains of the human papilloma virus that cause the majority of cervical cancers and genital warts. Merck has sold about 50 million doses worldwide, with more than $1.4 billion in revenue last year.

HPV infects about 6 million people in the U.S. each year, mainly through sexual contact. It usually causes no symptoms although rare cases can develop into warts and cancer in both men and women.

Merck has also asked the FDA to approve the vaccine for use in women ages 27-45. The FDA is continuing its review of that application.

In related news:

British drugmaker GlaxoSmithKline says U.S. regulators have approved its vaccine Cervarix to prevent the leading cause of cervical cancer in women.

The approval from the Food and Drug Administration allows Glaxo to compete against against Merck's blockbuster vaccine Gardasil, which has been on the market here since 2006.

Cervarix already is approved in nearly 100 other countries, but had been delayed in the U.S. since 2007, when the FDA requested additional data from the company.

The vaccine blocks the two main strains of the human papilloma virus that cause 75 percent of cervical cancer.