That may soon change. On Monday, scientists reported an important advance in the development of a long-acting antiretroviral shot. According to an international study involving 309 patients, an injection that combines two drugs, cabotegravir and rilpivirine, appears to be as safe and effective at suppressing HIV as the daily oral regimen.

Writing in the Lancet, David Margolis of ViiV Healthcare, called it “the next revolution in HIV therapy.”

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In the study, which was conducted at 50 centers in the United States, Germany, Canada, Spain, France and Germany, patients were begun on 20 weeks of daily oral medication. Once that medication had brought their viral loads down, they were given the shots as a “maintenance therapy.” Some were given the shot at four-week intervals and others at eight-week intervals. A control group continued to take the pills.

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The majority of the patients tolerated the therapy well, though nearly everyone reported some mild to moderate pain at the injection site. The rates of some adverse events like headaches were similar across all three groups.

At 96 weeks, 84 percent of the patients in the oral medication group were able to keep their viral load suppressed, compared with 87 percent of the four-week shot group and 94 percent of the eight-week shot group.

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The shots could revolutionize patient care in places like Africa, where it can be difficult for many people to get to a pharmacy regularly. But Mark A. Boyd, a professor at the University of Adelaide, wrote in a commentary piece accompanying the main article that there are trade-offs with both a pill and injection.

In his home country of Australia, for instance, he said people can get up to a six-month supply for antiretroviral pills. For them, going to a health-care provider for a monthly shot actually may be less convenient.

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“This is compounded by the fact that health-care systems are generally not configured to facilitate regular, recurrent injections in a timely and convenient way to people who are well,” he wrote. “Changing this will take innovation, political will and time.”

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Studies of some medications have shown dramatic increases in compliance and length of use with longer-acting versions versus daily pills. For osteoporosis drugs, for example, one study found compliance was just 38.6 percent for daily oral medications for a year and 77.7 percent for a monthly oral dose.

But for other therapies, a longer-acting formula doesn't seem to make a difference. While it has been difficult to compare compliance rates for birth control options because of varying methodology, one study involving postpartum teenagers found no difference in the rates (68 percent) at which they stopped using a monthly injectable and the pill.