Pre-exposure Prophylaxis (PrEP)
"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. As a preventive agent, the medication must be administered before exposure to the virus. As at 2022, there are three medications available in the market that can be used as PrEP (Diagram 1).
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 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.1
According to the WHO recommendation in 2022, while considering TDF/FTC as oral PrEP, people other than biological male without taking female hormone are only recommended to take it daily (“daily dosing” regimen). Biological male without taking female hormone having infrequent sex (Less than 2 days per week) may consider to take PrEP on as-needed basis, or consider switch from “daily dosing” regimen to “on-demand PrEP” regimen according to the frequency of sex.4
For other medications which can be used as PrEP, as existing research focus on certain high-risk persons, additional research is required to evaluate their efficacy of using in other people.2
Diagram 1: Market available PrEP (as at 2022)
Drug name | Contents | Route of administration |
Dosing regimen | Suitable for | Precautions concerning clients with specific background |
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Truvada® |
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Oral | Daily |
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On-demand |
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Descovy® |
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Oral | Daily |
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Vocabria® |
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Intramuscular injection | Every 8 weeks |
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Currently, the ingredients of PrEP can also be use as treatment purpose. Generally, adverse effects reported with PrEP are generally nonspecific and mild. In order to reduce the occurrence of severe side-effects, it is important to consult medical practitioner with through medical assessment including checking the possibility of PrEP interact with other medicines (also known as drug-drug interaction) before initiation of PrEP. Moreover, at least annual follow-up visits to review and monitor side-effects are recommended.
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:
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You will go through a detailed risk assessment to see if you have substantial risk of acquiring HIV infection, your doctor may ask you questions on your sexual history and related behaviours;
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You will go through a detailed medical assessment including an HIV test (4th generation HIV rapid test should be negative within 7 days before starting PrEP to rule out HIV infection), liver and renal function tests, screening for sexually transmitted infections (STIs), other blood tests as appropriate and your doctor may also ask about the medicines that you are taking to see if you are fit to take PrEP and the type of PrEP that is suit for you;
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Doctor will also discuss with you about other methods of HIV prevention, strategies for risk reduction and drug adherence.
Taking PrEP:
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You will be given a supply of PrEP for a period of no more than 3 months;
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You must take the drug/ have the injection on time;
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Adherence is very important to maintain good protection. You should think of ways to remind yourself to take the pill at around the same time every day, e.g. With a meal, before bed etc;
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Some side effects may trouble you in the initial few weeks. You may take the pill before bed. It may make it easier to get used to it;
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PrEP is an additional HIV prevention option that cannot replace condom use and it cannot prevent other sexually transmitted infections, so you should adopt usual risk reduction strategies and consistently use condoms.
Follow-up:
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Clients on PrEP should perform 4th generation HIV rapid test again within one month after initiation and every three months thereafter.
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In most cases, you will need to return to your doctor at least every 3 months or as instructed by your doctor. During subsequent revisits, the doctor will provide HIV test, STI screening and other related testing. Moreover, counselling for PrEP adherence and side effects, risk assessment, and prescription refills will also be provided.
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Even if you are taking an “on-demand PrEP” regimen and do not need to refill stock, you are still recommended to have follow up every three months (or as directed by your doctor) for HIV testing, STI screening and related testing, unless you do not have sex after last appointment.
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If you cannot adequately adhere to the medication regimen, your prescription will be discontinued.
Most clinical trials have shown that the effectiveness of PrEP for HIV prevention is dependent on medication adherence. When compared to “On-demand PrEP”, users of the“Daily dosing” regimen have a higher concentration of medication in their bodies. In general, persons who have sexual activity two or more days per week are advised to employ the "Daily dosing" regimen.
In the iPrEX research project, the simulation results showed that if users reduced their weekly dose from seven to four and two doses, the protective effect would drop from 99% to 96% and 76 % respectively. With a "Daily dosing" regimen, accidental missed doses will not negate protection.
- If you are a person who is suitable for“On-demand PrEP” (i.e. biological male without taking female hormone), the protective effect of PrEP will initiate if you have taken double dose of PrEP 2 hours prior to the sexual exposure. Then, you should take one dose per 24 hours. The maximum protective effect from HIV will reach at about 7 days of daily use. When you want to stop taking PrEP, you should ensure to stop after you have taken 2 consecutive doses from last potential sexual exposure to complete the protection.
- If you are not a person who is suitable for“On-demand PrEP” (e.g. biological female), you must start PrEP with one dose daily for seven consecutive days before sexual exposure to achieve protective effect and you must take one dose daily for seven days after last potential exposure to complete the protection.
Currently, only Truvada is available for “On-demand PrEP” regimen.
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 illustrates 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 Diagram 2)
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 Diagram 3)
Diagram 2: An “on-demand PrEP” (“2+1+1” dosing) regimen
Diagram 3: “On-demand PrEP” regimen if more sex acts take place over the following day.
If you are having“Daily dosing” regimen of PrEP, occasionally missing a dose for 1 to 2 days will not significantly reduce the efficacy of the drug, therefore, PEP is not required.
However, if you are having “On-demand PrEP” regimen, you must take PrEP on time. Missing pill may result in a drop of concentration of medication in your body that insufficient to protect you from HIV infection. If you are having unsafe sex at this time, you should visit a doctor to determine whether PEP is necessary.
Note: Avoid using PrEP and PEP at the same time.
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 or HIV positive with persistent undetectable viral level 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:
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Use condoms.
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Consider engaging in sex acts that have a lower risk of acquiring HIV, like oral sex.
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Get tested with your partners for HIV and other sexually transmitted infections.
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Encourage partners living with HIV to take their HIV medications every day.
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If alcohol or drugs are a problem, get help.
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If you inject drugs, always use a clean syringe.
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.
If you contract HIV while taking PrEP, the positive reaction may be different from usual situation. You are advised to attend HIV Specialist clinic as soon as possible. Taking PrEP alone is insufficient to treat HIV infection and it can result in drug resistance which limit the options of antiretroviral drugs for treatment in the future. Doctor may advise you to stop PrEP to observe and further tests will be done thereafter to determine whether you are infected and whether the virus is drug-resistant.
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.
PrEP has no contraceptive effect and can be taken safely with any hormonal contraception methods. PrEP can be used in pregnancy and during breastfeeding if HIV risk continues to be substantial during this time. According to experience in treatment HIV positive pregnant women, PrEP does not affect success pregnancy rate, cause congenital anomalies, growth retardation, abortion and preterm birth. Trace amount of drug can be found in breast milk but the amount does not affect infants’ health.1,3
Reference:
- WHO implementation tool for pre-exposure prophylaxis (PrEP) of HIV infection (Module Clinical) (July 2017)
- What's "2+1+1"? Event-driven oral pre-exposure prophylaxis to prevent HIV for men who have sex with men: Update to WHO's recommendation on oral PrEP
- Preventing HIV during pregnancy and breastfeeding in the context of PrEP
- Differentiated and simplified pre-exposure prophylaxis for HIV prevention: update to WHO implementation guidance (27 July 2022)