Implant in arm someday may block HIV for a year

In what could eventually become a milestone for HIV prevention, very preliminary tests of an implant containing a new drug suggest that it may protect against infection for a full year.

The new implant, by the drug company Merck, was tested in just a dozen subjects for 12 weeks. But experts were quite excited at its potential to revolutionize the long battle against HIV.

The research was described on Tuesday at an international AIDS conference in Mexico City.

New HIV prevention methods are desperately needed. About 75 million people have contracted the lethal virus since the AIDS epidemic began. Even now, about 1.7 million people are infected each year — despite decades of promotion of condoms and abstinence and years of efforts to get people to take a daily pill that prevents infection.

Dr. Robert M. Grant, a researcher at the University of California, San Francisco, who led the landmark 2010 trial that proved that a daily pill could thwart HIV, said he had expected a breakthrough based on the powerful new drug used in the implant.

Merck’s innovation is to deliver its new antiretroviral drug, islatravir, with a proven technology long used for birth control: a matchstick-sized plastic rod inserted just under the skin of the upper arm that slowly releases tiny doses of the medication.

Many people at risk of HIV infection are desperate for prevention methods that are easier to use, and easier to conceal, than a bottle of pills.

Islatravir has “some remarkable attributes,” said Dr. Roy D. Baynes, Merck’s chief medical officer.

It is 10 times as potent as any previous HIV drug, he said, so tiny amounts are effective, which lowers the risk of side effects. The drug lingers in the body for a relatively long time — after five days, half of the dose remains — so it can be given less often than other HIV medications.

Unlike some HIV drugs, islatravir is absorbed into anal and genital tissues, which is where most infections start.