Over the last decade, HIV treatment has been transformed. When a combination of drugs became the standard HIV treatment approach in the mid-1990s, many people took up to 20 pills, multiple times a day. Today, some people are using a drug regimen requiring one pill, once a day—a major breakthrough.
While there's no question that regimens consisting of the fewest number of pills, taken the fewest number of times a day, are highly appealing, regimens that are taken only once a day or involve just a couple of pills aren't necessarily easier or better than regimens taken twice a day or involve taking five or six pills.
For starters, a once-a-day drug means once every 24 hours, not once each day at whatever time you remember to take it—for example, one day with breakfast and the next day with lunch or dinner. Waiting too long between doses can cause drug levels to fluctuate in the body, which can lead to the development of drug resistance.
Also, some drugs are rapidly eliminated from the body, whereas others can linger in the bloodstream for many hours—even days. How quickly, or slowly, HIV drugs are processed in the body tells us how "forgiving" some treatment regimens may be if you do forget to take a dose on time once in a while. If you're taking a drug that achieves blood levels that remain above the minimum needed to keep HIV in control for hours after your next dose is due, then that drug is considered forgiving. If a drug rapidly falls below the necessary blood level shortly after the time of your next scheduled dose, it is considered to be less forgiving and requires strict adherence.
In the case of once-a-day dosing, some drugs are much more forgiving than others and this is an important consideration. Plus, a once-daily drug combination may contain both forgiving and less forgiving medications, so taking your medications on time, every time is important.
Results from studies comparing once- and twice-daily dosing, involving people with HIV and other diseases, have been mixed. Though people generally state a preference for once-daily dosing, not all studies have found that people who take drugs once a day have better adherence than people who take them twice a day.
Some experts have concerns that missed doses of a once-a-day drug may leave a person more at risk of developing resistance than missing doses of a drug taken twice a day (or more frequently). This is because blood levels of a drug can fall to dangerously low levels if a person skips a dose of a once-daily drug for an entire 24-hour period than if they only skipped the drug for an 8- or 12-hour period.
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