Apretude reaches its peak blood levels about one week after the first injection, and protective drug concentrations build within the first few days. However, the FDA states that the exact time from the first injection to maximum protection against HIV is unknown. Here’s what the available evidence tells us about the timeline and what to expect during the loading phase.
How Quickly Drug Levels Build
After your first injection, cabotegravir (the active drug in Apretude) is slowly absorbed from the gluteal muscle into your bloodstream. Blood levels reach their peak at a median of 7 days. But protective concentrations appear much sooner than that. Pharmacokinetic modeling shows that 80% of people reach meaningful protective thresholds within roughly 1 to 3 days after the first shot, depending on body composition and other individual factors.
That said, neither the FDA nor the CDC has established a specific day when you can consider yourself fully protected. The official language from both agencies is identical: the time to maximal protection is unknown. This doesn’t mean the drug isn’t working in those early days. It means no clinical trial was designed to pinpoint the exact moment protection kicks in, so agencies won’t put a number on it.
The Loading Phase Schedule
Apretude uses a two-injection loading phase to build up and sustain drug levels in your body. You receive your first injection, then a second injection four weeks later. After that, injections continue every two months (eight weeks) for as long as you want to stay on PrEP.
The second injection at the four-week mark is important. While your first shot gets drug levels up quickly, the second dose reinforces those levels before the drug from the first injection starts to decline. Once you’re on the every-two-month schedule, blood concentrations stay in a steady, protective range between injections. The drug has a long half-life of roughly 6 to 12 weeks, which is what makes the two-month dosing interval possible.
The Oral Lead-in Is Optional
When Apretude was first approved, the standard recommendation included taking a daily oral tablet for four weeks before your first injection. The purpose was to check whether you tolerate cabotegravir well before committing to a long-acting shot that stays in your system for months. If you had a bad reaction to the pill, you could simply stop taking it.
Current FDA labeling and CDC guidance make this oral lead-in optional. You and your provider can skip straight to the injection if you prefer. Data from HIV treatment trials using the same drug showed that skipping the oral lead-in didn’t reduce drug levels or change safety outcomes. For people who want protection to begin as soon as possible, going directly to the injection avoids a month-long waiting period on pills.
What This Means in Practice
Because there’s no officially defined “day one of full protection,” most clinicians advise using additional prevention methods (like condoms) during the early period after your first injection, particularly in the first week before peak levels are reached. This is a precautionary approach, not a reflection of evidence that the drug isn’t working during that window.
If you skip the oral lead-in and go straight to the injection, your body starts building protective drug levels immediately, with most people reaching key concentration thresholds within the first few days. If you do the optional four-week oral lead-in first, you’ll already have cabotegravir in your system before the injection, which means drug levels are present from day one of the shot.
Staying on Schedule
Keeping your injection appointments on time matters more with Apretude than with daily pills, where you can simply restart if you miss a stretch. Your second injection should happen as close to four weeks after the first as possible, and every subsequent injection should land near the eight-week mark. If you’re late, drug levels drop, and your provider may need to adjust your schedule or bridge with oral medication to maintain protection.
The long half-life of cabotegravir is a double-edged sword here. It keeps you protected between on-time injections, but it also means the drug lingers at low, non-protective levels for weeks after you stop. Those trailing low levels could theoretically allow HIV to develop resistance if you’re exposed during that window. So if you decide to stop Apretude, your provider will typically transition you to another form of PrEP to cover the tail period while the drug clears your system.