"PrEP" stands for pre-exposure prophylaxis. It generally means the use of an antiretroviral medication to prevent the acquisition of HIV infection by uninfected persons. Two antiretroviral drugs for treatment of HIV infection were approved for use as PrEP, oral dose of co-formulated tenofovir disoproxil fumarate plus emtricitabine (TDF/FTC) and tenofovir alafenamide plus emtricitabine (TAF/FTC). There are also ongoing studies of other antiretrovirals for prevention, including injectable and long acting agents. As preventive agents administered prior to exposure, they are collectively called pre-exposure prophylaxis (PrEP).
As at 2021, oral tenofovir disoproxil fumarate (TDF) 300 mg / emtricitabine (FTC) 200 mg is the drug most often adopted in countries with PrEP programmes. Unless otherwise stated, PrEP in this FAQ will henceforth refer to the administration of oral TDF/FTC to HIV negative individuals for the sole purpose of preventing acquisition of HIV.
PrEP is not recommended for everyone. According to World Health Organization (WHO), it can be considered for people who are HIV-negative and at substantial risk for HIV infection (HIV incidence per year > 3%). Each country or region should formulate own recommendations on PrEP use according to their situation and HIV epidemiology. Groups with known high HIV incidence usually include men who have sex with men (MSM) and transgender people who have sex with men, sex workers, people with a sexual partner who is HIV infected but non virally suppressed. People who inject drugs would be included in a few places while women in areas of high HIV incidence would also be included.
In Hong Kong, MSM with a history of unprotected receptive anal sex, use of recreational drugs, especially methamphetamine, or acquisition of syphilis in the previous six months are considered to be at elevated risks.
According to the WHO recommendation in 2019, while considering TDF/FTC as oral PrEP, people other than cisgender (refers to people whose gender identity matches the one they were assigned at birth) MSM are only recommended to take it daily (“daily dosing” regimen). MSM having infrequent sex may consider to take PrEP on as-needed basis, or consider switch from “daily dosing” regimen to “on-demand PrEP” regimen (details as below) according to the frequency of sex.
When using TAF/FTC as PrEP, “daily dosing” regimen is only recommended for cisgender MSM and transgender women who have sex with men. Additional research in other people is needed to evaluate the efficacy of using TAF/FTC as PrEP.
An "on-demand PrEP" regimen consists of at least four pills: two pills taken between 2 and 24 hours in advance of sex; one pill taken 24 hours after the first two pills and one pill taken 24 hours after the third pill. This regimen is also called “2+1+1” dosing. If sex acts happen in two or more days within a week, “daily dosing” regimen is recommended.
The following scenario illustrate how to take on-demand PrEP: If you take two tablets of Truvada on Jan 1st 8pm, the drug effect will start since 10pm. No matter what is the sex frequency or duration in that day, you must take one tablet on Jan 2nd 8pm. If no more sex is performed after 8pm, you need to take one more tablet on Jan 3rd 8pm, then you complete the on-demand PrEP. (See figure 1)
If you still have more sex after 8pm in day 2, you can extend PrEP for one more day. i.e. 2+1+1+1 (See figure 2)
Figure 1: An “on-demand PrEP” (“2+1+1” dosing) regimen
Figure 2: “On-demand PrEP” regimen if more sex acts take place over the following day.
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# "On-demand PrEP" regimen is not recommended for people living with chronic hepatitis B infection.
PrEP works only if it is taken. Many clinical trials revealed that the effect of prevention was highly dependent on the extent of adherence. In the iPrEX study, it was also shown by modeling that protection efficacy decreased from 99% at 7 doses per week to 96% at 4 doses per week and to 76% at 2 doses per week.
Studies showed that PrEP (including “on-demand PrEP”) starts protection from HIV when cisgender MSM taken first two pills TDF/FTC while PrEP reaches maximum protection at about 7 days of daily use. For other non-MSM populations, it takes 7 days after starting PrEP to build up protective levels of the medicine while PrEP reaches maximum protection at about 21 days of daily use.
The pill used for PrEP, Truvada®(contains FTC/TDF), has been used to treat people with HIV since 2004. The U.S. Food and Drug Administration (FDA) approved Truvada for PrEP use in 2012.
Adverse effects reported with PrEP are generally nonspecific and mild. However, renal function test was noted to be elevated and bone mineral density (BMD) decreased. In HIV infected patients, TDF/FTC is associated with liver and kidney complications. The possibility therefore exists that clinically significant toxicity may occur after prolonged use. The Centers for Disease Control and Prevention (CDC) recommends Descovy® (contains TAF/FTC) as PrEP for those who are at substantial risk of acquiring HIV infection and have preexisting impaired renal function or osteoporosis.
However, TDF and TAF are used for treating viral hepatitis B. For those who are chronically infected with hepatitis B, potential hepatitis flare on drug discontinuation is also cause for concern. This is particularly detrimental to those with cirrhosis. In many studies of PrEP, subjects with chronic hepatitis B were excluded. Therefore, there is lack of evidence to ensure that PrEP is safe for those infected with Hepatitis B. People with chronic hepatitis B should consult specialist for advice on the combined daily treatment of hepatitis B and PrEP. People without hepatitis B antibody should consider to be vaccinated.
Not only is TDF/FTC alone inadequate treatment of established HIV infection, it results in archived drug resistance which limits future antiretroviral option. It is therefore important that clients be put on PrEP only in the presence of a very recent negative HIV test and in the absence of seroconversion symptoms. The client should continue monitor if he/she have acquired HIV infection.
As at today, there is no public PrEP programme available in Hong Kong. You may get PrEP from registered private doctors or overseas doctors. You should consult medical practitioner with proper assessment before PrEP. The wholesale cost of the medication itself is currently around HK$6,000 per month. Please consult your doctors for the medication and related investigation cost they charge.
Pharmaceutical products and medicines imported of a person entering Hong Kong and which are accompanied by him and in a reasonable quantity for his personal use are permitted in Hong Kong. If you want to get PrEP overseas, you should choose reputable and qualified medical institutions for medical consultation before taking PrEP.
You need to consult a medical practitioner for proper assessment before taking PrEP.
Before taking PrEP, at the doctor's practice:
Not necessarily. PrEP is not a lifetime strategy. If you are no longer having high risk behaviour, say you find a long-term partner who's also HIV negative and you two decide to commit a monogamous relationship, then you may talk to your doctor for his opinion of stopping PrEP.
Yes. PrEP does not provide 100% protection against HIV. It serves to provide additional protection against HIV on top of the usual prevention methods you are using, not replacing it. Condoms also help protect against other sexually transmitted infections, like syphilis, gonorrhea genital warts.
For greater protection against HIV, combine PrEP with other ways to reduce HIV risk:
No, PrEP does not protect against other STIs. PrEP only reduces your risk of getting HIV. You should adopt your usual risk reduction strategies and consistently use condoms.
An increase in sexually transmitted infections (STI), probably due to an increase in unsafe sex practices after taking PrEP, has been observed among users of PrEP. In a meta-analysis of 18 cohort studies, occurrence of gonorrhoea, Chlamydia trachomatis infection and syphilis was found to be substantially increased (up to 45 times) for those MSM on PrEP. Its significance is three-fold. First, it portends that a rise in risk behaviour may occur with the use of PrEP. Second, untreated STI increases the risk of HIV infection and therefore has to be expeditiously treated in order not to undermine the effectiveness of PrEP. Third, it highlights the status of PrEP as being an additional option in a full prevention package, rather than a stand-alone measure.
Consult your doctor as soon as possible to get linked to HIV treatment and start anti-HIV therapy early to maintain your health. Also it's important to find someone to support and have people you can rely on with the emotional and physical challenges ahead.
A review in 2017 base on the Partners PrEP study (2011) found that 17% of people who acquired HIV while having sub-optimal PrEP adherence took more than 100 days to produce HIV antibodies. Therefore, for those who have sub-optimal PrEP adherence and get HIV infected, it significantly delays HIV infection detection.
Therefore, HIV testing by using the 4th generation HIV rapid test or conventional HIV testing for people taking PrEP should be checked regularly to exclude HIV infection no matter they take oral PrEP daily or as needed.