Pre-exposure prophylaxis, or PrEP, is a highly effective medication regimen designed to prevent HIV acquisition. It is intended for individuals who are HIV-negative but at risk of exposure to the virus. When taken as prescribed, PrEP works to protect the body by interfering with the HIV life cycle, thereby significantly reducing the chance of the virus establishing an infection. Its preventative power relies on consistent use, maintaining protective drug levels within the body.
How PrEP Protects the Body
PrEP medications, typically containing a combination of two antiretroviral drugs, function at a cellular level to block HIV. These active ingredients are nucleoside reverse transcriptase inhibitors (NRTIs). Once absorbed into the bloodstream, they travel to various tissues in the body, including genital and rectal tissues.
Within cells, these medications are converted into active forms that interfere with an enzyme called reverse transcriptase. HIV needs this enzyme to convert its RNA into DNA, a crucial step for the virus to replicate and establish a permanent infection. By inhibiting reverse transcriptase, PrEP prevents HIV from copying itself and spreading to other cells, effectively creating a biochemical shield.
Consequences of Skipping Doses
The impact of missing PrEP doses varies depending on the specific regimen and the number of doses skipped. For daily oral PrEP, the goal is to maintain a continuous protective concentration of the medication in the body. Missing even a single dose can slightly reduce drug levels, potentially lowering protection. While an occasional missed dose may not significantly reduce overall effectiveness, frequent missed doses can increase the risk of HIV acquisition.
Missing multiple doses significantly lowers drug concentrations, creating a vulnerability window where the body may not be adequately protected against HIV. For example, studies have shown that taking PrEP four times a week can result in a 96% reduction in HIV risk, while taking it only twice a week reduces effectiveness to 76%.
For event-driven PrEP, sometimes referred to as the “2-1-1 regimen,” the dosing schedule is specifically timed around sexual activity. This regimen involves taking pills before and after sexual activity according to a specific schedule. Missing any of these specific doses can immediately compromise protection, as this regimen relies on precise timing to achieve protective drug levels for anticipated exposures.
Guidance for Missed Doses
Clear steps exist for individuals who have missed PrEP doses to help maintain protection. If one daily PrEP dose is missed, it should be taken as soon as it is remembered. However, if it is almost time for the next scheduled dose, the missed dose should be skipped, and the regular dosing schedule should be continued. It is important not to double up on doses, as this does not provide additional benefit and can increase the likelihood of side effects.
If multiple doses of PrEP have been missed, it is important to contact a healthcare provider immediately. A healthcare provider can assess the individual situation, determine if an HIV test is necessary, and advise on the safest way to restart PrEP. If PrEP has been temporarily stopped for an extended period, it should not be restarted without medical consultation and a new HIV test to ensure HIV-negative status. Open communication with a healthcare provider about any missed doses or concerns is important for continued care.
Strategies for Consistent Use
Maintaining consistent PrEP use is an important factor in its effectiveness. Various practical strategies can help individuals adhere to their regimen and avoid missing doses. Setting daily reminders through phone alarms or dedicated apps can be highly effective. Linking dose-taking to routine daily activities, such as brushing teeth or eating a meal, can also help integrate PrEP into one’s schedule.
Using a weekly pill organizer provides a visual cue and helps track doses, making it easier to see if a pill has been missed. Planning for medication refills in advance helps prevent running out of medication and ensures a continuous supply. When traveling, it is important to plan ahead to ensure a sufficient supply of PrEP is available for the duration of the trip. Discussing any challenges with adherence with a healthcare provider or a trusted support person can also provide valuable support and solutions.