Pre-exposure prophylaxis, commonly known as PrEP, is a medication taken by individuals who do not have HIV to prevent acquiring the virus. This preventative strategy uses antiretroviral drugs to significantly reduce the risk of HIV infection before potential exposure. When taken as prescribed, PrEP can greatly reduce the chances of HIV transmission.
How PrEP Protects Against HIV
PrEP medications work by interfering with the Human Immunodeficiency Virus’s ability to replicate and establish an infection within the body. The commonly used oral PrEP regimens typically contain two active compounds, emtricitabine and tenofovir. These drugs are nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs).
When HIV enters the body, it attempts to convert its genetic material (RNA) into DNA using an enzyme called reverse transcriptase. Emtricitabine and tenofovir, once activated within cells, mimic the natural building blocks of DNA. The viral reverse transcriptase mistakenly incorporates these drug components into the newly forming viral DNA chain, leading to premature chain termination. This interruption prevents HIV from successfully replicating and integrating its genetic material into the host cell’s DNA, thereby blocking the infection from taking hold.
PrEP’s Effectiveness for Females: Addressing Misconceptions
PrEP is highly effective for females when taken consistently as prescribed. Misconceptions about its effectiveness often stem from early trial data where lower efficacy rates were observed in some groups of women, primarily due to challenges with adherence to the medication schedule. However, re-analyses of these studies and real-world data confirm that when PrEP is taken regularly, it provides substantial protection for cisgender women and transgender men.
One biological nuance previously considered was the concentration of PrEP drugs in different mucosal tissues. Tenofovir, a component of many oral PrEP formulations, was found to reach lower levels and take longer to achieve protective concentrations in vaginal and cervical tissues compared to rectal tissue. Despite these differences, current research demonstrates that adequate drug levels are achieved in vaginal tissue with consistent daily dosing, providing robust protection against HIV. For instance, oral PrEP pills reach maximum protection for receptive vaginal sex at about 21 days of daily use.
An analysis of combined data from post-marketing demonstration projects indicated that oral PrEP can be as effective for cisgender women as it is for men who have sex with men when adherence is high. Specifically, none of the cisgender women who took PrEP daily acquired HIV, and only one acquired HIV among those taking 4-6 doses per week. Moreover, a new injectable HIV prevention drug, lenacapavir, showed 100% effectiveness in a clinical study of cisgender women, with zero new diagnoses reported.
Factors Key to PrEP Success
The effectiveness of PrEP, regardless of an individual’s gender, relies heavily on consistent and correct adherence to the prescribed regimen. Taking the medication regularly ensures that sufficient drug levels are maintained in the body to block HIV infection. If PrEP is not taken as prescribed, its protective benefits are significantly reduced.
Missing multiple doses, especially within the initial weeks of starting PrEP, can compromise its ability to prevent HIV transmission. While missing an occasional single dose may not drastically impact overall protection, frequent missed doses increase the risk of infection. Establishing a routine, using reminders, and communicating any challenges with a healthcare provider can help maintain adherence.
Drug interactions can also influence PrEP’s success, though these are generally limited. Certain medications, such as some non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or diclofenac, or drugs for hepatitis C, can affect kidney function which PrEP can also impact. It is important to inform a healthcare provider about all medications, supplements, and other substances being used to ensure there are no adverse interactions that could reduce PrEP’s effectiveness or lead to side effects.
Available PrEP Options and Considerations
Several forms of PrEP are available, providing choices that can be tailored to individual lifestyles and preferences. Oral PrEP options include daily pills like Truvada (emtricitabine/tenofovir disoproxil fumarate) and Descovy (emtricitabine/tenofovir alafenamide). Truvada and its generic equivalents are approved for all people at risk through sex or injection drug use, including those engaging in receptive vaginal sex. Descovy, while highly effective, is not approved for people at risk for HIV through receptive vaginal sex, as its effectiveness in this population has not been fully evaluated.
Beyond daily oral pills, long-acting injectable PrEP options are now available. Apretude (cabotegravir extended-release injectable suspension) is an example, administered every two months after initial loading doses. This injectable form has been shown to be highly effective for cisgender women. Another injectable, Yeztugo (lenacapavir), is approved for twice-yearly administration.
The choice of PrEP medication depends on a person’s individual circumstances, including their specific risk factors for HIV, preferences for administration, and potential drug interactions. Consulting with a healthcare provider is essential to discuss the most suitable PrEP option, understand its benefits and limitations, and ensure it aligns with overall health needs.