PrEP: The Latest HIV Prevention Strategy
HIV drugs have long been used to prevent new infections in HIV-negative individuals.
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Post-exposure prophylaxis (PEP) is one strategy that involves the use of HIV drugs to prevent infection AFTER the person is exposed to the virus. In this case, the HIV medicines must be administered very soon after the exposure. Post-exposure prophylaxis was first developed to protect hospital and clinic workers from becoming infected after accidental needle-sticks with HIV-infected blood or from blood of a person whose HIV status was unknown.
In cases of rape, HIV meds may be used to protect the victim when the HIV status of the rapist is not known. Again, these meds must be taken very soon after the incident. In resource-poor countries that can’t afford to provide full HIV-treatment for pregnant women, HIV medicines are provided to the mother at the time of delivery to reduce the risk of infecting the new infant. This practice has dramatically reduced mother-to-child transmission of HIV.
Most recently, some very strategic studies have shown us that when an HIV-infected individual is faithfully taking their medicine, and their HIV in under control (undetectable levels of virus in the blood), their HIV-negative partner almost never gets infected – even without using male or female condoms.
Now, we’re talking about using drugs in HIV-negative people BEFORE they are exposed to HIV through unprotected sex with an infected person. This is called pre-exposure prophylaxis (PrEP). By this method, a person who is HIV-negative is taking medicines on a daily basis so that if they have sex with an infected person, the medicines are already in their tissues and can block HIV from infecting them.
Pre-exposure prophylaxis has been tested in many countries. In the US, the FDA-approved two potent HIV medicines combined in a single pill based on its ability to protect people at high risk for infection from being infected. The medicines Tenofovir (te-NO-FO-vir) and Emtricitibine (em-try-SY-toe-bean) are combined into a single pill product called Truvada (True-VA-da).
For HIV treatment, tenofovir and emtricibine must be combined with a third potent drug from a different class for maximal HIV suppression, yet taking this two-drug combo is effective for prevention. One study used pre-exposure prophylaxis in a group of HIV-negative MSM’s (men-who have sex-with men) who were having high rates of unprotected sex.
In this study those who were randomized to take the medicines had significantly lower rates of HIV infections than those not randomized to get the medicines. Another study looked at the use of PrEP in heterosexual couples where one partner was positive and the other partner negative. The negative partner gained significant protection from infection by taking pre-exposure prophylaxis.
As I stated above, the use of HIV medicines for treatment in the infected partner in a discordant couple (one partner is HIV+ and the other is HIV-) can protect the uninfected partner. However, the infected partner may not always take their medicines properly. Besides, there are other problems that can reduce the effect of the meds on transmitting the virus (such as having another STD). So by using PrEP, the negative partner has control over the situation by being able to protect themselves.
One of the biggest challenges in HIV management is getting patients to consistently take their medicine as prescribed. This remains the major reason why treatment regimens “fail” and HIV disease progresses.
So if HIV-infected patients don’t consistently take medicines to control their disease, why should we expect people who aren’t infected to do any better? In one study in Africa, women in South Africa were not well protected from HIV because their adherence to the medication regimen was poor. In the study of MSM’s, mentioned above, some of the men randomized to take PrEP became infected. Fortunately, in this study, the researchers measured the amount of drug in the patient’s tissues.
The men who got infected had practically no tenofovir or emtricibine in their tissues, indicating that they did not take their medicines reliably. This is why they got infected So we can say that PreP can work when the individuals actually take the drugs as prescribed.
When you take a medicine regularly as prescribed by your medical provider, the amount of the medicine in your blood and tissue hovers within a range of concentrations where it is effective. In medicine, we call this safe range the “steady state” concentration of the drug and it signals a level of good stability. However, taking medicines inconsistently results in wide variations in the amount of medicine in the blood and it frequently falls to concentrations too low to have an effect. These low levels would be unable to protect a person from an HIV infection.
How soon before the sexual encounter should the medicine be taken to have a protective effect? How long is a single dose effective before the concentration drops too low to work? We don’t know the answers to these questions, so people who use PrEP must be committed to take the medicine every day when they are sexually active.
The continuous dosing on Truvada creates another challenge. While this is a fairly safe regimen and easily tolerated by most patients, there are some possible side effects. The tenofovir component of the combo can have negative effects on the kidney. In a study presented at the International AIDS Conference last week, in Washington, DC, individuals who took the PrEP combo regularly had a slight decrease in bone density (mild osteoporosis), a known effect of tenofovir. These bone effects have been seen in other studies of PrEP and seem to be real effects but of minor medical significance. These side effects on the kidney and bone are easily detected and if they occur, a medical provider can stop the combo and reverse these problems.
Stopping the meds isn’t a problem because the individual doesn’t have HIV disease and doesn’t need the medicines for their personal health. However, they must be committed to getting regular medical exams if the plan to use PrEP.
One last medical issue: medication resistance. If a patient becomes infected while using PrEP (but not taking it properly), there’s a slight chance that the virus that infects them may be resistant to tenofovir and/or emtricitibine, meaning these drugs will not be available as treatment in this newly-infected person. For individuals who are HIV infected and not adherent to taking their medicines, they could already be resistant to tenofovir and/or emtricibine.
PrEP would provide no protection against being infected against such a person because their virus is already resistant to these medicines. I have seen cases where individuals were taking the combo (not prescribed by a medical provider!) and became infected. They may have gotten meds from the internet or from some other source and likely were not taking it regularly.
People who choose to use PrEP should have it prescribed after medical evaluation and discussion with their doctor and dispensed from a pharmacy. The doctor you choose should be experienced in the use of these drugs.
One last question: will your insurance pay for a drug used to treat a disease you don’t have? These medicines aren’t cheap! This is an important issue to consider.
So my final thought is that PrEP can be a potential tool in the fight to control the HIV epidemic. It gives power to the individual to protect themselves from HIV infection. However, there must be a commitment to take the medicines regularly as prescribed and the individual must get regular medical exams (which includes an HIV test!).